Devices and methods for low current neural modulation

ABSTRACT

A device may include an implantable circuit and at least one pair of implantable electrodes, in electrical communication with the implantable circuit. The circuit and the electrodes may configured for implantation in a subject in the vicinity of a nerve. The circuit may be configured to deliver to the electrodes an electrical signal having a current less than about 1.6 milliamps, and the electrodes may be configured to emit an electric field such that a portion of the field lines extend along a length of the nerve such that the delivery of the electrical signal of less than about 1.6 milliamps causes modulation of the nerve.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 13/629,748,filed Sep. 28, 2012, now U.S. Pat. No. 8,700,183, issued Nov. 5, 2013,which claims the benefit of priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 61/541,651, filed Sep. 30, 2011, and also toU.S. Provisional Application No. 61/657,424, filed Jun. 8, 2012, all ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to devices andmethods for modulating a nerve. More particularly, embodiments of thepresent disclosure relate to devices and methods for modulating a nervethrough the delivery of energy via an implantable electrical modulator.

BACKGROUND

Neural modulation presents the opportunity to treat many physiologicalconditions and disorders by interacting with the body's own naturalneural processes. Neural modulation includes inhibition (e.g. blockage),stimulation, modification, regulation, or therapeutic alteration ofactivity, electrical or chemical, in the central, peripheral, orautonomic nervous system. By modulating the activity of the nervoussystem, for example through the stimulation of nerves or the blockage ofnerve signals, several different goals may be achieved. Motor neuronsmay be stimulated at appropriate times to cause muscle contractions.Sensory neurons may be blocked, for instance to relieve pain, orstimulated, for instance to provide a signal to a subject. In otherexamples, modulation of the autonomic nervous system may be used toadjust various involuntary physiological parameters, such as heart rateand blood pressure. Neural modulation may provide the opportunity totreat several diseases or physiological conditions, a few examples ofwhich are described in detail below.

Among the conditions to which neural modulation may be applied isobstructive sleep apnea (OSA). OSA is a respiratory disordercharacterized by recurrent episodes of partial or complete obstructionof the upper airway during sleep. During the sleep of a person withoutOSA, the pharyngeal muscles relax during sleep and gradually collapse,narrowing the airway. The airway narrowing limits the effectiveness ofthe sleeper's breathing, causing a rise in CO₂ levels in the blood. Theincrease in CO₂ results in the pharyngeal muscles contracting to openthe airway to restore proper breathing. The largest of the pharyngealmuscles responsible for upper airway dilation is the genioglossusmuscle, which is one of several different muscles in the tongue. Thegenioglossus muscle is responsible for forward tongue movement and thestiffening of the anterior pharyngeal wall. In patients with OSA, theneuromuscular activity of the genioglossus muscle is decreased comparedto normal individuals, accounting for insufficient response andcontraction to open the airway as compared to a normal individual. Thislack of response contributes to a partial or total airway obstruction,which significantly limits the effectiveness of the sleeper's breathing.In OSA patients, there are often several airway obstruction eventsduring the night. Because of the obstruction, there is a gradualdecrease of oxygen levels in the blood (hypoxemia). Hypoxemia leads tonight time arousals, which may be registered by EEG, showing that thebrain awakes from any stage of sleep to a short arousal. During thearousal, there is a conscious breath or gasp, which resolves the airwayobstruction. An increase in sympathetic tone activity rate through therelease of hormones such as epinephrine and noradrenaline also oftenoccurs as a response to hypoxemia. As a result of the increase insympathetic tone, the heart enlarges in an attempt to pump more bloodand increase the blood pressure and heart rate, further arousing thepatient. After the resolution of the apnea event, as the patient returnsto sleep, the airway collapses again, leading to further arousals.

These repeated arousals, combined with repeated hypoxemia, leaves thepatient sleep deprived, which leads to daytime somnolence and worsenscognitive function. This cycle can repeat itself up to hundreds of timesper night in severe patients. Thus, the repeated fluctuations in andsympathetic tone and episodes of elevated blood pressure during thenight evolve to high blood pressure through the entire day.Subsequently, high blood pressure and increased heart rate may causeother diseases.

Efforts for treating OSA include Continuous Positive Airway Pressure(CPAP) treatment, which requires the patient to wear a mask throughwhich air is blown into the nostrils to keep the airway open. Othertreatment options include the implantation of rigid inserts in the softpalate to provide structural support, tracheotomies, or tissue ablation.

Another condition to which neural modulation may be applied is theoccurrence of migraine headaches. Pain sensation in the head istransmitted to the brain via the occipital nerve, specifically thegreater occipital nerve, and the trigeminal nerve. When a subjectexperiences head pain, such as during a migraine headache, theinhibition of these nerves may serve to decrease or eliminate thesensation of pain.

Neural modulation may also be applied to hypertension. Blood pressure inthe body is controlled via multiple feedback mechanisms. For example,baroreceptors in the carotid body in the carotid artery are sensitive toblood pressure changes within the carotid artery. The baroreceptorsgenerate signals that are conducted to the brain via theglossopharyngeal nerve when blood pressure rises, signaling the brain toactivate the body's regulation system to lower blood pressure, e.g.through changes to heart rate, and vasodilation/vasoconstriction.Conversely, parasympathetic nerve fibers on and around the renalarteries generate signals that are carried to the kidneys to initiateactions, such as salt retention and the release of angiotensin, whichraise blood pressure. Modulating these nerves may provide the ability toexert some external control over blood pressure.

The foregoing are just a few examples of conditions to whichneuromodulation may be of benefit, however embodiments of the inventiondescribed hereafter are not necessarily limited to treating only theabove-described conditions.

SUMMARY

A device according to some embodiments may include an implantablecircuit and at least one pair of implantable electrodes electricallyconnected with the implantable circuit. The circuit and the electrodesmay be configured for implantation in a subject proximal to agenioglossus muscle in the vicinity of a hypoglossal nerve. The circuitmay be configured to deliver to the electrodes an electrical signalhaving a current less than about 1.6 milliamps, and the electrodes maybe configured to emit an electric field such that a portion of the fieldlines extend along a length of the hypoglossal nerve such that thedelivery of the electrical signal of less than about 1.6 milliampscauses modulation of the hypoglossal nerve.

A device according to some embodiments may include an implantablecircuit and at least one pair of implantable electrodes electricallyconnected with the implantable circuit. The circuit and the electrodesmay be configured for implantation in a subject in the vicinity of anerve. The circuit may be configured to deliver to the electrodes anelectrical signal having a current less than about 1.6 milliamps, andthe electrodes may be configured to emit an electric field such that aportion of the field lines extend along a length of the nerve such thatthe delivery of the electrical signal of less than about 1.6 milliampscauses modulation of the nerve.

A device according to some embodiments may include an implantablecircuit and at least one pair of implantable electrodes configured to beimplanted beneath the skin of a subject in a substantially haired regionin the vicinity of an occipital nerve of a subject. The device mayinclude an antenna configured to receive a signal and to be implantedbeneath the skin of the subject in a substantially hairless region. Theimplantable electrodes may be electrically connected with a first end ofthe implantable circuit and the antenna may be electrically connectedwith a second end of the implantable circuit. In addition, the circuitmay be configured to deliver to the electrodes an electrical signalhaving a current less than about 1.6 milliamps, and the electrodes maybe configured to emit an electric field such that a portion of the fieldlines extend along a length of the nerve such that the delivery of theelectrical signal of less than about 1.6 milliamps causes modulation ofthe nerve.

A device according to some embodiments may include an implantablecircuit and at least one pair of implantable electrodes electricallyconnected with the implantable circuit. The circuit and the electrodesmay be configured for implantation in a subject in a blood vessel in thevicinity of at least one of a renal nerve, a carotid baroreceptor, and aglossopharyngeal nerve. The circuit may be configured to deliver to theelectrodes an electrical signal having a current less than about 1.6milliamps, and the electrodes may be configured to emit an electricfield such that a portion of the field lines extend along a length ofthe nerve such that the delivery of the electrical signal of less thanabout 1.6 milliamps causes modulation of the at least one of a renalnerve, a carotid baroreceptor, and a glossopharyngeal nerve.

Some embodiments may include a method of stimulating a nerve via atleast one pair of electrodes associated with an implanted circuit andimplanted in the vicinity of the nerve. The method may includedelivering to the electrodes, via the implanted circuit, an electricalsignal having a current less than about 1.6 milliamps. The method mayfurther include stimulating the nerve via the generation of anelectrical field between the electrodes by the electrical signal havinga current less than about 1.6 milliamps.

Additional features of the disclosure will be set forth in part in thedescription that follows, and in part will be obvious from thedescription, or may be learned by practice of the disclosed embodiments.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of thedisclosure and, together with the description, serve to explain theprinciples of the embodiments disclosed herein.

FIG. 1 schematically illustrates an implant unit and external unit,according to an exemplary embodiment of the present disclosure.

FIG. 2 is a partially cross-sectioned side view of a subject with animplant unit and external unit, according to an exemplary embodiment ofthe present disclosure.

FIG. 3 schematically illustrates a system including an implant unit andan external unit, according to an exemplary embodiment of the presentdisclosure.

FIG. 4 is a top view of an implant unit, according to an exemplaryembodiment of the present disclosure.

FIG. 5 is a top view of an alternate embodiment of an implant unit,according to an exemplary embodiment of the present disclosure.

FIG. 6 illustrates circuitry of an implant unit and an external unit,according to an exemplary embodiment of the present disclosure.

FIG. 7 illustrates a graph of quantities that may be used in determiningenergy delivery as a function coupling, according to an exemplarydisclosed embodiment.

FIG. 8 depicts a graph illustrating non-linear harmonics.

FIG. 9 depicts a graph of quantities that may be used in determiningenergy delivery as a function coupling, according to an exemplarydisclosed embodiment.

FIG. 10a illustrates a pair of electrodes spaced apart from one anotheralong the longitudinal direction of nerve to facilitate generation of anelectric field having field lines substantially parallel to thelongitudinal direction of nerve.

FIG. 10b illustrates an embodiment wherein electrodes are spaced apartfrom one another in a longitudinal direction of at least a portion ofnerve.

FIG. 10c illustrates a situation wherein electrodes are spaced apartfrom one another in a transverse direction of nerve.

FIG. 11 illustrates affects of electrode configuration on the shape of agenerated electric field.

FIG. 12 depicts anatomy of the tongue and associated muscles and nerves.

FIG. 13 depicts an exemplary implant location for the treatment of sleepapnea.

FIG. 14 depicts an exemplary implant location for the treatment of headpain.

FIG. 15 depicts an exemplary implant location for the treatment ofhypertension.

FIG. 16 depicts an exemplary implant location for the treatment ofhypertension.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Reference will now be made in detail to exemplary embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Embodiments of the present disclosure relate generally to a device formodulating a nerve through the delivery of energy. Nerve modulation, orneural modulation, includes inhibition (e.g. blockage), stimulation,modification, regulation, or therapeutic alteration of activity,electrical or chemical, in the central, peripheral, or autonomic nervoussystem. Nerve modulation may take the form of nerve stimulation, whichmay include providing energy to the nerve to create a voltage changesufficient for the nerve to activate, or propagate an electrical signalof its own. Nerve modulation may also take the form of nerve inhibition,which may including providing energy to the nerve sufficient to preventthe nerve from propagating electrical signals. Nerve inhibition may beperformed through the constant application of energy, and may also beperformed through the application of enough energy to inhibit thefunction of the nerve for some time after the application. Other formsof neural modulation may modify the function of a nerve, causing aheightened or lessened degree of sensitivity. As referred to herein,modulation of a nerve may include modulation of an entire nerve and/ormodulation of a portion of a nerve. For example, modulation of a motorneuron may be performed to affect only those portions of the neuron thatare distal of the location to which energy is applied.

In patients with OSA, for example, a primary target response of nervestimulation may include contraction of a tongue muscle (e.g., themuscle) in order to move the tongue to a position that does not blockthe patient's airway. In the treatment of migraine headaches, nerveinhibition may be used to reduce or eliminate the sensation of pain. Inthe treatment of hypertension, neural modulation may be used toincrease, decrease, eliminate or otherwise modify nerve signalsgenerated by the body to regulate blood pressure.

While embodiments of the present disclosure may be disclosed for use inpatients with specific conditions, the embodiments may be used inconjunction with any patient/portion of a body where nerve modulationmay be desired. That is, in addition to use in patients with OSA,migraine headaches, or hypertension, embodiments of the presentdisclosure may be use in many other areas, including, but not limitedto: deep brain stimulation (e.g., treatment of epilepsy, Parkinson's,and depression); cardiac pace-making, stomach muscle stimulation (e.g.,treatment of obesity), back pain, incontinence, menstrual pain, and/orany other condition that may be affected by neural modulation.

FIG. 1 illustrates an implant unit and external unit, according to anexemplary embodiment of the present disclosure. An implant unit 110, maybe configured for implantation in a subject, in a location that permitsit to modulate a nerve 115. The implant unit 110 may be located in asubject such that intervening tissue 111 exists between the implant unit110 and the nerve 115. Intervening tissue may include muscle tissue,connective tissue, organ tissue, or any other type of biological tissue.Thus, location of implant unit 110 does not require contact with nerve115 for effective neuromodulation. A more detailed discussion ofnon-contacting neuromodulation is provided below with respect to FIGS.10a, 10b, 10c , and 11. The implant unit 110 may also be locateddirectly adjacent to nerve 115, such that no intervening tissue 111exists.

In treating OSA, implant unit 110 may be located on a genioglossusmuscle of a patient. Such a location is suitable for modulation of thehypoglossal nerve, branches of which run inside the genioglossus muscle.Further details regarding implantation locations of an implant unit 110for treatment of OSA are provided below with respect to FIGS. 12 and 13.Implant unit 110 may also be configured for placement in otherlocations. For example, migraine treatment may require subcutaneousimplantation in the back of the neck, near the hairline of a subject, orbehind the ear of a subject, to modulate the greater occipital nerve,lesser occipital nerve, and/or the trigeminal nerve. Further detailsregarding implantation locations of an implant unit 110 for treatment ofhead pain, such as migraine headaches, are provided below with respectto FIG. 14. Treating hypertension may require the implantation of aneuromodulation implant intravascularly inside the renal artery or renalvein (to modulate the parasympathetic renal nerves), either unilaterallyor bilaterally, inside the carotid artery or jugular vein (to modulatethe glossopharyngeal nerve through the carotid baroreceptors).Alternatively or additionally, treating hypertension may require theimplantation of a neuromodulation implant subcutaneously, behind the earor in the neck, for example, to directly modulate the glossopharyngealnerve. Further details regarding implantation locations of an implantunit 110 for treatment of hypertension are provided below, with respectto FIGS. 15 and 16.

External unit 120 may be configured for location external to a patient,either directly contacting, or close to the skin 112 of the patient.External unit 120 may be configured to be affixed to the patient, forexample, by adhering to the skin 112 of the patient, or through a bandor other device configured to hold external unit 120 in place. Adherenceto the skin of external unit 120 may occur such that it is in thevicinity of the location of implant unit 110.

FIG. 2 illustrates an exemplary embodiment of a neuromodulation systemfor delivering energy in a patient 100 with OSA. The system may includean external unit 120 that may be configured for location external to thepatient. As illustrated in FIG. 2, external unit 120 may be configuredto be affixed to the patient 100. FIG. 2 illustrates that in a patient100 with OSA, the external unit 120 may be configured for placementunderneath the patient's chin and/or on the front of patient's neck. Thesuitability of placement locations may be determined by communicationbetween external unit 120 and implant unit 110, discussed in greaterdetail below. In alternate embodiments, for the treatment of conditionsother than OSA, the external unit may be configured to be affixedanywhere suitable on a patient, such as the back of a patient's neck,i.e. for communication with a migraine treatment implant unit, on theouter portion of a patient's abdomen, i.e. for communication with astomach modulating implant unit, on a patient's back, i.e. forcommunication with a renal artery modulating implant unit, and/or on anyother suitable external location on a patient's skin, depending on therequirements of a particular application.

External unit 120 may further be configured to be affixed to analternative location proximate to the patient. For example, in oneembodiment, the external unit may be configured to fixedly or removablyadhere to a strap or a band that may be configured to wrap around a partof a patient's body. Alternatively, or in addition, the external unitmay be configured to remain in a desired location external to thepatient's body without adhering to that location.

The external unit 120 may include a housing. The housing may include anysuitable container configured for retaining components. In addition,while the external unit is illustrated schematically in FIG. 2, thehousing may be any suitable size and/or shape and may be rigid orflexible. Non-limiting examples of housings for the external unit 100include one or more of patches, buttons, or other receptacles havingvarying shapes and dimensions and constructed of any suitable material.In one embodiment, for example, the housing may include a flexiblematerial such that the external unit may be configured to conform to adesired location. For example, as illustrated in FIG. 2, the externalunit may include a skin patch, which, in turn, may include a flexiblesubstrate. The material of the flexible substrate may include, but isnot limited to, plastic, silicone, woven natural fibers, and othersuitable polymers, copolymers, and combinations thereof. Any portion ofexternal unit 120 may be flexible or rigid, depending on therequirements of a particular application.

As previously discussed, in some embodiments external unit 120 may beconfigured to adhere to a desired location. Accordingly, in someembodiments, at least one side of the housing may include an adhesivematerial. The adhesive material may include a biocompatible material andmay allow for a patient to adhere the external unit to the desiredlocation and remove the external unit upon completion of use. Theadhesive may be configured for single or multiple uses of the externalunit. Suitable adhesive materials may include, but are not limited tobiocompatible glues, starches, elastomers, thermoplastics, andemulsions.

FIG. 3 schematically illustrates a system including external unit 120and an implant unit 110. In some embodiments, internal unit 110 may beconfigured as a unit to be implanted into the body of a patient, andexternal unit 120 may be configured to send signals to and/or receivesignals from implant unit 110.

As shown in FIG. 3, various components may be included within a housingof external unit 120 or otherwise associated with external unit 120. Asillustrated in FIG. 3, at least one processor 144 may be associated withexternal unit 120. For example, the at least one processor 144 may belocated within the housing of external unit 120. In alternativeembodiments, the at least one processor may be configured for wired orwireless communication with the external unit from a location externalto the housing.

The at least one processor may include any electric circuit that may beconfigured to perform a logic operation on at least one input variable.The at least one processor may therefore include one or more integratedcircuits, microchips, microcontrollers, and microprocessors, which maybe all or part of a central processing unit (CPU), a digital signalprocessor (DSP), a field programmable gate array (FPGA), or any othercircuit known to those skilled in the art that may be suitable forexecuting instructions or performing logic operations.

FIG. 3 illustrates that the external unit 120 may further be associatedwith a power source 140. The power source may be removably couplable tothe external unit at an exterior location relative to external unit.Alternatively, as shown in FIG. 3, power source 140 may be permanentlyor removably coupled to a location within external unit 120. The powersource may further include any suitable source of power configured to bein electrical communication with the processor. In one embodiment, forexample the power source 140 may include a battery.

The power source may be configured to power various components withinthe external unit. As illustrated in FIG. 3, power source 140 may beconfigured to provide power to the processor 144. In addition, the powersource 140 may be configured to provide power to a signal source 142.The signal source 142 may be in communication with the processor 144 andmay include any device configured to generate a signal (e.g., asinusoidal signal, square wave, triangle wave, microwave,radio-frequency (RF) signal, or any other type of electromagneticsignal). Signal source 142 may include, but is not limited to, awaveform generator that may be configured to generate alternatingcurrent (AC) signals and/or direct current (DC) signals. In oneembodiment, for example, signal source 142 may be configured to generatean AC signal for transmission to one or more other components. Signalsource 142 may be configured to generate a signal of any suitablefrequency. In some embodiments, signal source 142 may be configured togenerate a signal having a frequency of from about 6.5 MHz to about 13.6MHz. In additional embodiments, signal source 142 may be configured togenerate a signal having a frequency of from about 7.4 to about 8.8 MHz.In further embodiments, signal source 142 may generate a signal having afrequency as low as 90 kHz or as high as 28 MHz.

Signal source 142 may be configured for direct or indirect electricalcommunication with an amplifier 146. The amplifier may include anysuitable device configured to amplify one or more signals generated fromsignal source 142. Amplifier 146 may include one or more of varioustypes of amplification devices, including, for example, transistor baseddevices, operational amplifiers, RF amplifiers, power amplifiers, or anyother type of device that can increase the gain associated one or moreaspects of a signal. The amplifier may further be configured to outputthe amplified signals to one or more components within external unit120.

The external unit may additionally include a primary antenna 150. Theprimary antenna may be configured as part of a circuit within externalunit 120 and may be coupled either directly or indirectly to variouscomponents in external unit 120. For example, as shown in FIG. 3,primary antenna 150 may be configured for communication with theamplifier 146.

The primary antenna may include any conductive structure that may beconfigured to create an electromagnetic field. The primary antenna mayfurther be of any suitable size, shape, and/or configuration. The size,shape, and/or configuration may be determined by the size of thepatient, the placement location of the implant unit, the size and/orshape of the implant unit, the amount of energy required to modulate anerve, a location of a nerve to be modulated, the type of receivingelectronics present on the implant unit, etc. The primary antenna mayinclude any suitable antenna known to those skilled in the art that maybe configured to send and/or receive signals. Suitable antennas mayinclude, but are not limited to, a long-wire antenna, a patch antenna, ahelical antenna, etc. In one embodiment, for example, as illustrated inFIG. 3, primary antenna 150 may include a coil antenna. Such a coilantenna may be made from any suitable conductive material and may beconfigured to include any suitable arrangement of conductive coils(e.g., diameter, number of coils, layout of coils, etc.). A coil antennasuitable for use as primary antenna 150 may have a diameter of betweenabout 1 cm and 10 cm, and may be circular or oval shaped. In someembodiments, a coil antenna may have a diameter between 5 cm and 7 cm,and may be oval shaped. A coil antenna suitable for use as primaryantenna 150 may have any number of windings, e.g. 4, 8, 12, or more. Acoil antenna suitable for use as primary antenna 150 may have a wirediameter between about 0.1 mm and 2 mm. These antenna parameters areexemplary only, and may be adjusted above or below the ranges given toachieve suitable results.

As noted, implant unit 110 may be configured to be implanted in apatient's body (e.g., beneath the patient's skin). FIG. 2 illustratesthat the implant unit 110 may be configured to be implanted formodulation of a nerve associated with a muscle of the subject's tongue130. Modulating a nerve associated with a muscle of the subject's tongue130 may include stimulation to cause a muscle contraction. In furtherembodiments, the implant unit may be configured to be placed inconjunction with any nerve that one may desire to modulate. For example,modulation of the occipital nerve, the greater occipital nerve, and/orthe trigeminal nerve may be useful for treating pain sensation in thehead, such as that from migraines. Modulation of parasympathetic nervefibers on and around the renal arteries (i.e. the renal nerves), thevagus nerve, and/or the glossopharyngeal nerve may be useful fortreating hypertension. Additionally, any nerve of the peripheral nervoussystem (both spinal and cranial), including motor neurons, sensoryneurons, sympathetic neurons and parasympathetic neurons, may bemodulated to achieve a desired effect.

Implant unit 110 may be formed of any materials suitable forimplantation into the body of a patient. In some embodiments, implantunit 110 may include a flexible carrier 161 (FIG. 4) including aflexible, biocompatible material. Such materials may include, forexample, silicone, polyimides, phenyltrimethoxysilane (PTMS), polymethylmethacrylate (PMMA), Parylene C, polyimide, liquid polyimide, laminatedpolyimide, black epoxy, polyether ether ketone (PEEK), Liquid CrystalPolymer (LCP), Kapton, etc. Implant unit 110 may further includecircuitry including conductive materials, such as gold, platinum,titanium, or any other biocompatible conductive material or combinationof materials. Implant unit 110 and flexible carrier 161 may also befabricated with a thickness suitable for implantation under a patient'sskin. Implant 110 may have thickness of less than about 4 mm or lessthan about 2 mm.

Other components that may be included in or otherwise associated withthe implant unit are illustrated in FIG. 3. For example, implant unit110 may include a secondary antenna 152 mounted onto or integrated withflexible carrier 161. Similar to the primary antenna, the secondaryantenna may include any suitable antenna known to those skilled in theart that may be configured to send and/or receive signals. The secondaryantenna may include any suitable size, shape, and/or configuration. Thesize, shape and/or configuration may be determined by the size of thepatient, the placement location of the implant unit, the amount ofenergy required to modulate the nerve, etc. Suitable antennas mayinclude, but are not limited to, a long-wire antenna, a patch antenna, ahelical antenna, etc. In some embodiments, for example, secondaryantenna 152 may include a coil antenna having a circular shape (see alsoFIG. 4) or oval shape. Such a coil antenna may be made from any suitableconductive material and may be configured to include any suitablearrangement of conductive coils (e.g., diameter, number of coils, layoutof coils, etc.). A coil antenna suitable for use as secondary antenna152 may have a diameter of between about 5 mm and 30 mm, and may becircular or oval shaped. A coil antenna suitable for use as secondaryantenna 152 may have any number of windings, e.g. 4, 15, 20, 30, or 50.A coil antenna suitable for use as secondary antenna 152 may have a wirediameter between about 0.01 mm and 1 mm. These antenna parameters areexemplary only, and may be adjusted above or below the ranges given toachieve suitable results.

Implant unit 110 may additionally include a plurality offield-generating implant electrodes 158 a, 158 b. The electrodes mayinclude any suitable shape and/or orientation on the implant unit solong as the electrodes may be configured to generate an electric fieldin the body of a patient. Implant electrodes 158 a and 158 b may alsoinclude any suitable conductive material (e.g., copper, silver, gold,platinum, iridium, platinum-iridium, platinum-gold, conductive polymers,etc.) or combinations of conductive (and/or noble metals) materials. Insome embodiments, for example, the electrodes may include short lineelectrodes, circular electrodes, and/or circular pairs of electrodes. Asshown in FIG. 4, electrodes 158 a and 158 b may be located on an end ofa first extension 162 a of an elongate arm 162. The electrodes, however,may be located on any portion of implant unit 110. Additionally, implantunit 110 may include electrodes located at a plurality of locations, forexample on an end of both a first extension 162 a and a second extension162 b of elongate arm 162, as illustrated, for example, in FIG. 5.Implant electrodes may have a thickness between about 200 nanometers and1 millimeter. Anode and cathode electrode pairs may be spaced apart byabout a distance of about 0.2 mm to 25 mm. In additional embodiments,anode and cathode electrode pairs may be spaced apart by a distance ofabout 1 mm to 10 mm, or between 4 mm and 7 mm. In other embodiments,anode and cathode electrode pairs may be spaced apart by a distance ofapproximately 6 mm. Adjacent anodes or adjacent cathodes may be spacedapart by distances as small as 0.001 mm or less, or as great as 25 mm ormore. In some embodiments, adjacent anodes or adjacent cathodes may bespaced apart by a distance between about 0.2 mm and 1 mm.

FIG. 4 provides a schematic representation of an exemplary configurationof implant unit 110. As illustrated in FIG. 4, in one embodiment, thefield-generating electrodes 158 a and 158 b may include two sets of fourcircular electrodes, provided on flexible carrier 161, with one set ofelectrodes providing an anode and the other set of electrodes providinga cathode. Implant unit 110 may include one or more structural elementsto facilitate implantation of implant unit 110 into the body of apatient. Such elements may include, for example, elongated arms, sutureholes, polymeric surgical mesh, biological glue, spikes of flexiblecarrier protruding to anchor to the tissue, spikes of additionalbiocompatible material for the same purpose, etc. that facilitatealignment of implant unit 110 in a desired orientation within apatient's body and provide attachment points for securing implant unit110 within a body. For example, in some embodiments, implant unit 110may include an elongate arm 162 having a first extension 162 a and,optionally, a second extension 162 b. Extensions 162 a and 162 b may aidin orienting implant unit 110 with respect to a particular muscle (e.g.,the genioglossus muscle), a nerve within a patient's body, or a surfacewithin a body above a nerve. For example, first and second extensions162 a, 162 b may be configured to enable the implant unit to conform atleast partially around soft or hard tissue (e.g., nerve, bone, ormuscle, etc.) beneath a patient's skin. Further, implant unit 110 mayalso include one or more suture holes 160 located anywhere on flexiblecarrier 161. For example, in some embodiments, suture holes 160 may beplaced on second extension 162 b of elongate arm 162 and/or on firstextension 162 a of elongate arm 162. Implant unit 110 may be constructedin various shapes. In some embodiments, implant unit may appearsubstantially as illustrated in FIG. 4. In other embodiments, implantunit 110 may lack illustrated structures such as second extension 162 b,or may have additional or different structures in differentorientations. Additionally, implant unit 110 may be formed with agenerally triangular, circular, or rectangular shape, as an alternativeto the winged shape shown in FIG. 4. In some embodiments, the shape ofimplant unit 110 (e.g., as shown in FIG. 4) may facilitate orientationof implant unit 110 with respect to a particular nerve to be modulated.Thus, other regular or irregular shapes may be adopted in order tofacilitate implantation in differing parts of the body.

As illustrated in FIG. 4, secondary antenna 152 and electrodes 158 a,158 b may be mounted on or integrated with flexible carrier 161. Variouscircuit components and connecting wires (discussed further below) may beused to connect secondary antenna with implant electrodes 158 a and 158b. To protect the antenna, electrodes, circuit components, andconnecting wires from the environment within a patient's body, implantunit 110 may include a protective coating that encapsulates implant unit110. In some embodiments, the protective coating may be made from aflexible material to enable bending along with flexible carrier 161. Theencapsulation material of the protective coating may also resisthumidity penetration and protect against corrosion. In some embodiments,the protective coating may include silicone, polyimides,phenyltrimethoxysilane (PTMS), polymethyl methacrylate (PMMA), ParyleneC, liquid polyimide, laminated polyimide, polyimide, Kapton, blackepoxy, polyether ketone (PEEK), Liquid Crystal Polymer (LCP), or anyother suitable biocompatible coating. In some embodiments, theprotective coating may include a plurality of layers, includingdifferent materials or combinations of materials in different layers.

FIG. 5 is a perspective view of an alternate embodiment of an implantunit 110, according to an exemplary embodiment of the presentdisclosure. As illustrated in FIG. 5, implant unit 110 may include aplurality of electrodes, located, for example, at the ends of firstextension 162 a and second extension 162 b. FIG. 5 illustrates anembodiment wherein implant electrodes 158 a and 158 b include short lineelectrodes.

Returning to FIGS. 2 and 3, external unit 120 may be configured tocommunicate with implant unit 110. For example, in some embodiments, aprimary signal may be generated on primary antenna 150, using, e.g.,processor 144, signal source 142, and amplifier 146. More specifically,in one embodiment, power source 140 may be configured to provide powerto one or both of the processor 144 and the signal source 142. Theprocessor 144 may be configured to cause signal source 142 to generate asignal (e.g., an RF energy signal). Signal source 142 may be configuredto output the generated signal to amplifier 146, which may amplify thesignal generated by signal source 142. The amount of amplification and,therefore, the amplitude of the signal may be controlled, for example,by processor 144. The amount of gain or amplification that processor 144causes amplifier 146 to apply to the signal may depend on a variety offactors, including, but not limited to, the shape, size, and/orconfiguration of primary antenna 150, the size of the patient, thelocation of implant unit 110 in the patient, the shape, size, and/orconfiguration of secondary antenna 152, a degree of coupling betweenprimary antenna 150 and secondary antenna 152 (discussed further below),a desired magnitude of electric field to be generated by implantelectrodes 158 a, 158 b, etc. Amplifier 146 may output the amplifiedsignal to primary antenna 150.

External unit 120 may communicate a primary signal on primary antenna tothe secondary antenna 152 of implant unit 110. This communication mayresult from coupling between primary antenna 150 and secondary antenna152. Such coupling of the primary antenna and the secondary antenna mayinclude any interaction between the primary antenna and the secondaryantenna that causes a signal on the secondary antenna in response to asignal applied to the primary antenna. In some embodiments, couplingbetween the primary and secondary antennas may include capacitivecoupling, inductive coupling, radiofrequency coupling, etc. and anycombinations thereof.

Coupling between primary antenna 150 and secondary antenna 152 maydepend on the proximity of the primary antenna relative to the secondaryantenna. That is, in some embodiments, an efficiency or degree ofcoupling between primary antenna 150 and secondary antenna 152 maydepend on the proximity of the primary antenna to the secondary antenna.The proximity of the primary and secondary antennas may be expressed interms of a coaxial offset (e.g., a distance between the primary andsecondary antennas when central axes of the primary and secondaryantennas are co-aligned), a lateral offset (e.g., a distance between acentral axis of the primary antenna and a central axis of the secondaryantenna), and/or an angular offset (e.g., an angular difference betweenthe central axes of the primary and secondary antennas). In someembodiments, a theoretical maximum efficiency of coupling may existbetween primary antenna 150 and secondary antenna 152 when both thecoaxial offset, the lateral offset, and the angular offset are zero.Increasing any of the coaxial offset, the lateral offset, and theangular offset may have the effect of reducing the efficiency or degreeof coupling between primary antenna 150 and secondary antenna 152.

As a result of coupling between primary antenna 150 and secondaryantenna 152, a secondary signal may arise on secondary antenna 152 whenthe primary signal is present on the primary antenna 150. Such couplingmay include inductive/magnetic coupling, RF coupling/transmission,capacitive coupling, or any other mechanism where a secondary signal maybe generated on secondary antenna 152 in response to a primary signalgenerated on primary antenna 150. Coupling may refer to any interactionbetween the primary and secondary antennas. In addition to the couplingbetween primary antenna 150 and secondary antenna 152, circuitcomponents associated with implant unit 110 may also affect thesecondary signal on secondary antenna 152. Thus, the secondary signal onsecondary antenna 152 may refer to any and all signals and signalcomponents present on secondary antenna 152 regardless of the source.

While the presence of a primary signal on primary antenna 150 may causeor induce a secondary signal on secondary antenna 152, the couplingbetween the two antennas may also lead to a coupled signal or signalcomponents on the primary antenna 150 as a result of the secondarysignal present on secondary antenna 152. A signal on primary antenna 150induced by a secondary signal on secondary antenna 152 may be referredto as a primary coupled signal component. The primary signal may referto any and all signals or signal components present on primary antenna150, regardless of source, and the primary coupled signal component mayrefer to any signal or signal component arising on the primary antennaas a result of coupling with signals present on secondary antenna 152.Thus, in some embodiments, the primary coupled signal component maycontribute to the primary signal on primary antenna 150.

Implant unit 110 may be configured to respond to external unit 120. Forexample, in some embodiments, a primary signal generated on primary coil150 may cause a secondary signal on secondary antenna 152, which inturn, may cause one or more responses by implant unit 110. In someembodiments, the response of implant unit 110 may include the generationof an electric field between implant electrodes 158 a and 158 b.

FIG. 6 illustrates circuitry 170 that may be included in external unit120 and circuitry 180 that may be included in implant unit 110.Additional, different, or fewer circuit components may be included ineither or both of circuitry 170 and circuitry 180. As shown in FIG. 6,secondary antenna 152 may be arranged in electrical communication withimplant electrodes 158 a, 158 b. In some embodiments, circuitryconnecting secondary antenna 152 with implant electrodes 158 a and 158 bmay cause a voltage potential across implant electrodes 158 a and 158 bin the presence of a secondary signal on secondary antenna 152. Thisvoltage potential may be referred to as a field inducing signal, as thisvoltage potential may generate an electric field between implantelectrodes 158 a and 158 b. More broadly, the field inducing signal mayinclude any signal (e.g., voltage potential) applied to electrodesassociated with the implant unit that may result in an electric fieldbeing generated between the electrodes.

The field inducing signal may be generated as a result of conditioningof the secondary signal by circuitry 180. As shown in FIG. 6, circuitry170 of external unit 120 may be configured to generate an AC primarysignal on primary antenna 150 that may cause an AC secondary signal onsecondary antenna 152. In certain embodiments, however, it may beadvantageous (e.g., in order to generate a unidirectional electric fieldfor modulation of a nerve) to provide a DC field inducing signal atimplant electrodes 158 a and 158 b. To convert the AC secondary signalon secondary antenna 152 to a DC field inducing signal, circuitry 180 inimplant unit 110 may include an AC-DC converter. The AC to DC convertermay include any suitable converter known to those skilled in the art.For example, in some embodiments the AC-DC converter may includerectification circuit components including, for example, diode 156 andappropriate capacitors and resistors. In alternative embodiments,implant unit 110 may include an AC-AC converter, or no converter, inorder to provide an AC field inducing signal at implant electrodes 158 aand 158 b.

As noted above, the field inducing signal may be configured to generatean electric field between implant electrodes 158 a and 158 b. In someinstances, the magnitude and/or duration of the generated electric fieldresulting from the field inducing signal may be sufficient to modulateone or more nerves in the vicinity of electrodes 158 a and 158 b. Insuch cases, the field inducing signal may be referred to as a modulationsignal. In other instances, the magnitude and/or duration of the fieldinducing signal may generate an electric field that does not result innerve modulation. In such cases, the field inducing signal may bereferred to as a sub-modulation signal.

Various types of field inducing signals may constitute modulationsignals. For example, in some embodiments, a modulation signal mayinclude a moderate amplitude and moderate duration, while in otherembodiments, a modulation signal may include a higher amplitude and ashorter duration. Various amplitudes and/or durations of field-inducingsignals across electrodes 158 a, 158 b may result in modulation signals,and whether a field-inducing signal rises to the level of a modulationsignal can depend on many factors (e.g., distance from a particularnerve to be stimulated; whether the nerve is branched; orientation ofthe induced electric field with respect to the nerve; type of tissuepresent between the electrodes and the nerve; etc.).

The generation of electric fields configured to penetrate interveningtissue is now discussed with respect to FIGS. 10a, 10b, 10c , and 11. Inresponse to a field inducing signal, implant electrodes 158 a and 158 bmay be configured to generate an electric field with field linesextending generally in the longitudinal direction of one or more nervesto be modulated. In some embodiments, implant electrodes 158 a and 158 bmay be spaced apart from one another along the longitudinal direction ofa nerve to facilitate generation of such an electric field. The electricfield may also be configured to extend in a direction substantiallyparallel to a longitudinal direction of at least some portion of thenerve to be modulated. For example, a substantially parallel field mayinclude field lines that extend more in a longitudinal direction than atransverse direction compared to the nerve. Orienting the electric fieldin this way may facilitate electrical current flow through a nerve ortissue, thereby increasing the likelihood of eliciting an actionpotential to induce modulation.

FIG. 10a illustrates a pair of electrodes 158 a, 158 b spaced apart fromone another along the longitudinal direction of nerve 210 to facilitategeneration of an electric field having field lines 220 substantiallyparallel to the longitudinal direction of nerve 210. In FIG. 10a ,modulation electrodes 158 a, 158 b are illustrated as line electrodes,although the generation of substantially parallel electric fields may beaccomplished through the use of other types of electrodes, for example,a series of point electrodes. Utilizing an electric field having fieldlines 220 extending in a longitudinal direction of nerve 210 may serveto reduce the amount of energy required to achieve neural modulation.

Naturally functioning neurons function by transmitting action potentialsalong their length. Structurally, neurons include multiple ion channelsalong their length that serve to maintain a voltage potential gradientacross a plasma membrane between the interior and exterior of theneuron. Ion channels operate by maintaining an appropriate balancebetween positively charged sodium ions on one side of the plasmamembrane and negatively charged potassium ions on the other side of theplasma membrane. A sufficiently high voltage potential differencecreated near an ion channel may exceed a membrane threshold potential ofthe ion channel. The ion channel may then be induced to activate,pumping the sodium and potassium ions across the plasma membrane toswitch places in the vicinity of the activated ion channel. This, inturn, further alters the potential difference in the vicinity of the ionchannel, which may serve to activate a neighboring ion channel. Thecascading activation of adjacent ion channels may serve to propagate anaction potential along the length of the neuron. Further, the activationof an ion channel in an individual neuron may induce the activation ofion channels in neighboring neurons that, bundled together, form nervetissue. The activation of a single ion channel in a single neuron,however, may not be sufficient to induce the cascading activation ofneighboring ion channels necessary to permit the propagation of anaction potential. Thus, the more ion channels in a locality that may berecruited by an initial potential difference, caused through naturalmeans such as the action of nerve endings or through artificial means,such as the application of electric fields, the more likely thepropagation of an action potential may be. The process of artificiallyinducing the propagation of action potentials along the length of anerve may be referred to as stimulation, or up modulation.

Neurons may also be prevented from functioning naturally throughconstant or substantially constant application of a voltage potentialdifference. After activation, each ion channel experiences a refractoryperiod, during which it “resets” the sodium and potassium concentrationsacross the plasma membrane back to an initial state. Resetting thesodium and potassium concentrations causes the membrane thresholdpotential to return to an initial state. Until the ion channel restoresan appropriate concentration of sodium and potassium across the plasmamembrane, the membrane threshold potential will remain elevated, thusrequiring a higher voltage potential to cause activation of the ionchannel. If the membrane threshold potential is maintained at a highenough level, action potentials propagated by neighboring ion channelsmay not create a large enough voltage potential difference to surpassthe membrane threshold potential and activate the ion channel. Thus, bymaintaining a sufficient voltage potential difference in the vicinity ofa particular ion channel, that ion channel may serve to block furthersignal transmission. The membrane threshold potential may also be raisedwithout eliciting an initial activation of the ion channel. If an ionchannel (or a plurality of ion channels) are subjected to an elevatedvoltage potential difference that is not high enough to surpass themembrane threshold potential, it may serve to raise the membranethreshold potential over time, thus having a similar effect to an ionchannel that has not been permitted to properly restore ionconcentrations. Thus, an ion channel may be recruited as a block withoutactually causing an initial action potential to propagate. This methodmay be valuable, for example, in pain management, where the propagationof pain signals is undesired. As described above with respect tostimulation, the larger the number of ion channels in a locality thatmay be recruited to serve as blocks, the more likely the chance that anaction potential propagating along the length of the nerve will beblocked by the recruited ion channels, rather than traveling throughneighboring, unblocked channels.

The number of ion channels recruited by a voltage potential differencemay be increased in at least two ways. First, more ion channels may berecruited by utilizing a larger voltage potential difference in a localarea. Second, more ion channels may be recruited by expanding the areaaffected by the voltage potential difference.

Returning to FIG. 10a , it can be seen that, due to the electric fieldlines 220 running in a direction substantially parallel to thelongitudinal direction of the nerve 210, a large portion of nerve 210may encounter the field. Thus, more ion channels from the neurons thatmake up nerve 210 may be recruited without using a larger voltagepotential difference. In this way, modulation of nerve 210 may beachieved with a lower current and less power usage. FIG. 10b illustratesan embodiment wherein electrodes 158 a and 158 are still spaced apartfrom one another in a longitudinal direction of at least a portion ofnerve 210. A significant portion of nerve 210 remains inside of theelectric field. FIG. 10c illustrates a situation wherein electrodes 158a and 158 b are spaced apart from one another in a transverse directionof nerve 210. In this illustration, it can be seen that a significantlysmaller portion of nerve 210 will be affected by electric field lines220.

FIG. 11 illustrates potential effects of electrode configuration on theshape of a generated electric field. The top row of electrodeconfigurations, e.g. A, B, and C, illustrates the effects on theelectric field shape when a distance between electrodes of a constantsize is adjusted. The bottom row of electrode configurations, e.g. D, E,and F illustrates the effects on the electric field shape when the sizeof electrodes of constant distance is adjusted.

In embodiments consistent with the present disclosure, modulationelectrodes 158 a, 158 b may be arranged on the surface of a muscle orother tissue, in order to modulate a nerve embedded within the muscle orother tissue. Thus, tissue may be interposed between modulationelectrodes 158 a, 158 b and a nerve to be modulated. Modulationelectrodes 158 a, 158 b may be spaced away from a nerve to be modulated.The structure and configuration of modulation electrodes 158 a, 158 bmay play an important role in determining whether modulation of a nerve,which is spaced a certain distance away from the electrodes, may beachieved.

Electrode configurations A, B, and C show that when modulationelectrodes 158 a, 158 b of a constant size are moved further apart, thedepth of the electric field facilitated by the electrodes increases. Thestrength of the electric field for a given configuration may varysignificantly depending on a location within the field. If a constantlevel of current is passed between modulation electrodes 158 a and 158b, however, the larger field area of configuration C may exhibit a loweroverall current density than the smaller field area of configuration A.A lower current density, in turn, implies a lower voltage potentialdifference between two points spaced equidistant from each other in thefield facilitated by configuration C relative to that of the fieldfacilitated by configuration A. Thus, while moving modulation electrodes158 a and 158 b farther from each other increases the depth of thefield, it also decreases the strength of the field. In order to modulatea nerve spaced away from modulation electrodes 158 a, 158 b, a distancebetween the electrodes may be selected in order to facilitate anelectric field of strength sufficient to surpass a membrane thresholdpotential of the nerve (and thereby modulate it) at the depth of thenerve. If modulation electrodes 158 a, 158 b are too close together, theelectric field may not extend deep enough into the tissue in order tomodulate a nerve located therein. If modulation electrodes 158 a, 158 bare too far apart, the electric field may be too weak to modulate thenerve at the appropriate depth.

Appropriate distances between modulation electrodes 158 a, 158 b, maydepend on an implant location and a nerve to be stimulated. For example,modulation point 901 is located at the same depth equidistant from thecenters of modulation electrodes 158 a, 158 b in each of configurationsA, B, and C. The figures illustrate that, in this example, configurationB is most likely to achieve the highest possible current density, andtherefore voltage potential, at modulation point 901. The field ofconfiguration A may not extend deeply enough, and the field ofconfiguration C may be too weak at that depth.

In some embodiments, modulation electrodes 158 a, 158 b may be spacedapart by about a distance of about 0.2 mm to 25 mm. In additionalembodiments, modulation electrodes 158 a, 158 b may be spaced apart by adistance of about 1 mm to 10 mm, or between 4 mm and 7 mm. In otherembodiments modulation electrodes 158 a, 158 b may be spaced apart bybetween approximately 6 mm and 7 mm.

Electrode configurations D, E, and F show that when modulationelectrodes 158 a, 158 b of a constant distance are changed in size, theshape of the electric field facilitated by the electrodes changes. If aconstant level of current is passed between when modulation electrodes158 a and 158 b, the smaller electrodes of configuration D mayfacilitate a deeper field than that of configurations E and F, althoughthe effect is less significant relative to changes in distance betweenthe electrodes. As noted above, the facilitated electric fields are notof uniform strength throughout, and thus the voltage potential atseemingly similar locations within each of the electric fields ofconfigurations D, E, and, F may vary considerably. Appropriate sizes ofmodulation electrodes 158 a, 158 b, may therefore depend on an implantlocation and a nerve to be stimulated.

In some embodiments, modulation electrodes 158 a, 158 b may have asurface area between approximately 0.01 mm² and 80 mm². In additionalembodiments, modulation electrodes 158 a, 158 b may have a surface areabetween approximately 0.1 mm² and 4 mm². In other embodiments modulationelectrodes 158 a, 158 b may have a surface area of between approximately0.25 mm² and 0.35 mm².

In some embodiments, modulation electrodes 158 a, 158 b may be arrangedsuch that the electrodes are exposed on a single side of carrier 161. Insuch an embodiment, an electric field is generated only on the side ofcarrier 161 with exposed electrodes. Such a configuration may serve toreduce the amount of energy required to achieve neural modulation,because the entire electric field is generated on the same side of thecarrier as the nerve, and little or no current is wasted travelingthrough tissue away from the nerve to be modulated. Such a configurationmay also serve to make the modulation more selective. That is, bygenerating an electric field on the side of the carrier where there is anerve to be modulated, nerves located in other areas of tissue (e.g. onthe other side of the carrier from the nerve to be modulated), may avoidbeing accidentally modulated.

As discussed above, the utilization of electric fields having electricalfield lines extending in a direction substantially parallel to thelongitudinal direction of a nerve to be modulated may serve to lower thepower requirements of modulation. This reduction in power requirementsmay permit the modulation of a nerve using less than 1.6 mA of current,less than 1.4 mA of current, less than 1.2 mA of current, less than 1 mAof current, less than 0.8 mA of current, less than 0.6 mA of current,less than 0.4 mA of current, and even less than 0.2 mA of current passedbetween modulation electrodes 158 a, 158 b.

Reducing the current flow required may have additional effects on theconfiguration of implant unit 110 and external unit 120. For example,the reduced current requirement may enable implant unit 110 to modulatea nerve without a requirement for a power storage unit, such as abattery or capacitor, to be implanted in conjunction with implant unit110. For example, implant unit 110 may be capable of modulating a nerveusing only the energy received via secondary antenna 152. Implant unit110 may be configured to serve as a pass through that directssubstantially all received energy to modulation electrodes 158 a and 158b for nerve modulation. Substantially all received energy may refer tothat portion of energy that is not dissipated or otherwise lost to theinternal components of implant unit 110. Finally, the reduction inrequired current may also serve to reduce the amount of energy requiredby external unit 120. External unit 120 may be configured to operatesuccessfully for an entire treatment session lasting from one to tenhours by utilizing a battery having a capacity of less than 240 mAh,less than 120 mAh, and even less than 60 mAh.

As discussed above, utilization of parallel fields may enable implantunit 110 to modulate nerves in a non-contacting fashion. Contactlessneuromodulation may increase the efficacy of an implanted implant unit110 over time compared to modulation techniques requiring contact with anerve or muscle to be modulated. Over time, implantable devices maymigrate within the body. Thus, an implantable device requiring nervecontact to initiate neural modulation may lose efficacy as the devicemoves within the body and loses contact with the nerve to be modulated.In contrast, implant unit 110, utilizing contactless modulation, maystill effectively modulate a nerve even if it moves away from an initialimplant location. Additionally, tissue growth and/or fibrosis maydevelop around an implantable device. This growth may serve to lessen oreven eliminate the contact between a device designed for contactmodulation and a nerve to be modulated. In contrast, implant unit 110,utilizing contactless modulation, may continue to effectively modulate anerve if additional tissue forms between it and a nerve to be modulated.

As discussed above, utilization of parallel fields may enable implantunit 110 to modulate nerves in a non-contacting fashion. Contactlessneuromodulation may increase the efficacy of an implanted implant unit110 over time compared to modulation techniques requiring contact with anerve or muscle to be modulated. Over time, implantable devices maymigrate within the body. Thus, an implantable device requiring nervecontact to initiate neural modulation may lose efficacy as the devicemoves within the body and loses contact with the nerve to be modulated.In contrast, implant unit 110, utilizing contactless modulation, maystill effectively modulate a nerve even if it moves toward, away, or toanother location relative to an initial implant location. Additionally,tissue growth and/or fibrosis may develop around an implantable device.This growth may serve to lessen or even eliminate the contact between adevice designed for contact modulation and a nerve to be modulated. Incontrast, implant unit 110, utilizing contactless modulation, maycontinue to effectively modulate a nerve if additional tissue formsbetween it and a nerve to be modulated.

As described above, modulation electrodes 158 a, 158 b, of implant unit110 may be configured so as to facilitate the generation of an electricfield sufficient to modulate a nerve even when a voltage signal of lowcurrent is applied to modulation electrodes 158 a, 158 b. In someembodiments consistent with the present disclosure, implant unit 110 mayhave no means of measuring the current of a voltage signal applied tomodulation electrodes 158 a, 158 b. In such an embodiment, processor 144may be configured to supply a voltage signal having a specific currentvalue, for example, less than about 1.6 mAmps, as follows. Processor 144may be configured to adjust the characteristics, for example, thevoltage, of a primary signal. Processor 144 may detect coupling betweenprimary antenna 152 and secondary antenna 162, and therefore determinethe voltage of the secondary signal induced on the secondary antenna 162by the primary signal. The voltage induced in the implant may drive acertain amount of current through the circuitry 180 of the implant tomodulation electrodes 158 a, 158 b. The amount of current driven throughthe implant unit 110 may depend on the voltage of the secondary signal,the configuration of implant circuitry 180, and the resistance betweenmodulation electrodes 158 a, 158 b. The resistance between modulationelectrodes 158 a, 158 b, may vary for physiological reasons becausetissue closes the circuit. Implant positioning, tissue composition,tissue hydration, and other physiological factors may all affect theresistance, and thus the current across the electrodes. The resistance,however, will vary within a small range, and the known factors, such asimplant circuitry 180, may dominate these small variations. Thus,processor 144 may be configured with information about a configurationof implant unit 110, modulation electrodes, 158 a, 158 b, and ranges ofvariation of tissue impedance so as to be able to adjust the primarysignal to an appropriate voltage in order to deliver the specifiedamount of current to modulation electrodes 158 a, 158 b in order tomodulate a nerve.

The circuitry 180 of implant unit 110 may also be configured to deliverto the electrodes an electrical signal having a current less than about1.6 milliamps. That is, the design of the implant circuitry 180, thevalues of the resistors, capacitors, diodes, and other electroniccomponents of implant circuitry 180 may be chosen specifically such thatwhen a primary signal on primary antenna 152 induces a secondary signalon secondary antenna 162, the voltage of the secondary signal will besufficient to drive the specified amount of current across modulationelectrodes 158 a, 158 b, in order to modulate a nerve.

Whether a field inducing signal constitutes a modulation signal(resulting in an electric field that may cause nerve modulation) or asub-modulation signal (resulting in an electric field not intended tocause nerve modulation) may ultimately be controlled by processor 144 ofexternal unit 120. For example, in certain situations, processor 144 maydetermine that nerve modulation is appropriate. Under these conditions,processor 144 may cause signal source 144 and amplifier 146 to generatea modulation control signal on primary antenna 150 (i.e., a signalhaving a magnitude and/or duration selected such that a resultingsecondary signal on secondary antenna 152 will provide a modulationsignal at implant electrodes 158 a and 158 b).

In some embodiments, a modulation signal resulting in neural stimulationmay be provided by electrodes 158 a and 158 b in response to one or moreelectrical signals (e.g. signals having various voltage levels, currentlevels, or durations) supplied by circuitry 180. Such stimulation mayresult even when each supplied electrical signal has a current of lessthan about 1 millliamp. In such embodiments, electrodes 158 a and 158 bmay be configured to emit an electric field such that at least a portionof the field lines extend along a length of the nerve such that thedelivery of the electrical signal of less than about 1.6 milliampscauses stimulation of the nerve. Circuitry 180 (including variouscapacitor values, diode activation potentials, etc.) may be configuredto deliver a substantial portion of the energy received from externalunit 120 to the subject within about 1 second or less of receiving theenergy.

As discussed above, implant unit 110 may be secured to the surface ofnon-nerve tissue. One or more of muscle tissue, connective tissue, fat,blood vessel, and mucosal membrane may be interposed between theelectrodes and the nerve. The electrodes may be configured to generatean electric field sufficient to stimulate the underlying nerve with lessthan 1.6 milliamps of current.

Processor 144 may be configured to limit an amount of energy transferredfrom external unit 120 to implant unit 110. For example, in someembodiments, implant unit 110 may be associated with a threshold energylimit that may take into account multiple factors associated with thepatient and/or the implant. For example, in some cases, certain nervesof a patient should receive no more than a predetermined maximum amountof energy to minimize the risk of damaging the nerves and/or surroundingtissue. Additionally, circuitry 180 of implant unit 110 may includecomponents having a maximum operating voltage or power level that maycontribute to a practical threshold energy limit of implant unit 110.For example, components including diodes may be included in implant unit110 or in external unit 120 to limit power transferred from the externalunit 120 to the implant unit 110. In some embodiments, diode 156 mayfunction to limit the power level received by the patient. Processor 144may be configured to account for such limitations when setting themagnitude and/or duration of a primary signal to be applied to primaryantenna 150.

In addition to determining an upper limit of power that may be deliveredto implant unit 110, processor 144 may also determine a lower powerthreshold based, at least in part, on an efficacy of the deliveredpower. The lower power threshold may be computed based on a minimumamount of power that enables nerve modulation (e.g., signals havingpower levels above the lower power threshold may constitute modulationsignals while signals having power levels below the lower powerthreshold may constitute sub-modulation signals).

A lower power threshold may also be measured or provided in alternativeways. For example, appropriate circuitry or sensors in the implant unit110 may measure a lower power threshold. A lower power threshold may becomputed or sensed by an additional external device, and subsequentlyprogrammed into processor 144, or programmed into implant unit 110.Alternatively, implant unit 110 may be constructed with circuitry 180specifically chosen to generate signals at the electrodes of at leastthe lower power threshold. In still another embodiment, an antenna ofexternal unit 120 may be adjusted to accommodate or produce a signalcorresponding to a specific lower power threshold. The lower powerthreshold may vary from patient to patient, and may take into accountmultiple factors, such as, for example, modulation characteristics of aparticular patient's nerve fibers, a distance between implant unit 110and external unit 120 after implantation, and the size and configurationof implant unit components (e.g., antenna and implant electrodes), etc.

Processor 144 may also be configured to cause application ofsub-modulation control signals to primary antenna 150. Suchsub-modulation control signals may include an amplitude and/or durationthat result in a sub-modulation signal at electrodes 158 a, 158 b. Whilesuch sub-modulation control signals may not result in nerve modulation,such sub-modulation control signals may enable feedback-based control ofthe nerve modulation system. That is, in some embodiments, processor 144may be configured to cause application of a sub-modulation controlsignal to primary antenna 150. This signal may induce a secondary signalon secondary antenna 152, which, in turn, induces a primary coupledsignal component on primary antenna 150.

To analyze the primary coupled signal component induced on primaryantenna 150, external unit 120 may include a feedback circuit 148 (e.g.,a signal analyzer or detector, etc.), which may be placed in direct orindirect communication with primary antenna 150 and processor 144.Sub-modulation control signals may be applied to primary antenna 150 atany desired periodicity. In some embodiments, the sub-modulation controlsignals may be applied to primary antenna 150 at a rate of one everyfive seconds (or longer). In other embodiments, the sub-modulationcontrol signals may be applied more frequently (e.g., once every twoseconds, once per second, once per millisecond, once per nanosecond, ormultiple times per second). Further, it should be noted that feedbackmay also be received upon application of modulation control signals toprimary antenna 150 (i.e., those that result in nerve modulation), assuch modulation control signals may also result in generation of aprimary coupled signal component on primary antenna 150.

The primary coupled signal component may be fed to processor 144 byfeedback circuit 148 and may be used as a basis for determining a degreeof coupling between primary antenna 150 and secondary antenna 152. Thedegree of coupling may enable determination of the efficacy of theenergy transfer between two antennas. Processor 144 may also use thedetermined degree of coupling in regulating delivery of power to implantunit 110.

Processor 144 may be configured with any suitable logic for determininghow to regulate power transfer to implant unit 110 based on thedetermined degree of coupling. Processor 144 may, for example, utilize abaseline coupling range. Presumably, while the patient is awake, thetongue is not blocking the patient's airway and moves with the patient'sbreathing in a natural range, where coupling between primary antenna 150and secondary antenna 152 may be within a baseline coupling range. Abaseline coupling range may encompass a maximum coupling between primaryantenna 150 and secondary antenna 152. A baseline coupling range mayalso encompass a range that does not include a maximum coupling levelbetween primary antenna 150 and secondary antenna 152. Processor 144 maybe configured to determine the baseline coupling range based on acommand from a user, such as the press of a button on the patch or thepress of a button on a suitable remote device. Alternatively oradditionally, processor 144 may be configured to automatically determinethe baseline coupling range when external unit 120 is placed such thatprimary antenna 150 and secondary antenna 152 are within range of eachother. In such an embodiment, when processor 144 detects any degree ofcoupling between primary antenna 150 and secondary antenna 152, it mayimmediately begin tracking a baseline coupling range. Processor 144 maythen determine a baseline coupling range when it detects that the onlymovement between primary antenna 150 and secondary antenna 152 is causedby a patient's natural breathing rhythm (i.e., the patient has securedthe external unit to an appropriate location on their body).Additionally, processor 144 may be configured such that it measurescoupling between the primary antenna 150 and the secondary antenna 152for a specified period of time after activation in order to determine abaseline coupling range, such as 1 minute, 5 minutes, 10 minutes, etc.

Where the primary coupled signal component indicates that a degree ofcoupling has changed from a baseline coupling range, processor 144 maydetermine that secondary antenna 152 has moved with respect to primaryantenna 150 (either in coaxial offset, lateral offset, or angularoffset, or any combination). Such movement, for example, may beassociated with a movement of the implant unit 110, and the tissue thatit is associated with based on its implant location. Thus, in suchsituations, processor 144 may determine that modulation of a nerve inthe patient's body is appropriate. More particularly, in response to anindication of a change in coupling, processor 144, in some embodiments,may cause application of a modulation control signal to primary antenna150 in order to generate a modulation signal at implant electrodes 158a, 158 b, e.g., to cause modulation of a nerve of the patient.

In an embodiment for the treatment of OSA, movement of an implant unit110 may be associated with movement of the tongue, which may indicatethe onset of a sleep apnea event or a sleep apnea precursor. The onsetof a sleep apnea event of sleep apnea precursor may require thestimulation of the genioglossus muscle of the patient to relieve oravert the event. Such stimulation may result in contraction of themuscle and movement of the patient's tongue away from the patient'sairway.

In embodiments for the treatment of head pain, including migraines,processor 144 may be configured to generate a modulation control signalbased on a signal from a user, for example, or a detected level ofneural activity in a sensory neuron (e.g. the greater occipital nerve ortrigeminal nerve) associated with head pain. A modulation control signalgenerated by the processor and applied to the primary antenna 150 maygenerate a modulation signal at implant electrodes 158 a, 158 b, e.g.,to cause inhibition or blocking (i.e. a down modulation) of a sensorynerve of the patient. Such inhibition or blocking may decrease oreliminate the sensation of pain for the patient.

In embodiments for the treatment of hypertension, processor 144 may beconfigured to generate a modulation control signal based on, forexample, pre-programmed instructions and/or signals from an implantindicative of blood pressure. A modulation control signal generated bythe processor and applied to the primary antenna 150 may generate amodulation signal at implant electrodes 158 a, 158 b, e.g., to causeeither inhibition or stimulation of nerve of a patient, depending on therequirements. For example, a neuromodulator placed in a carotid arteryor jugular vein (i.e. in the vicinity of a carotid baroreceptor), mayreceive a modulation control signal tailored to induce a stimulationsignal at the electrodes, thereby causing the glossopharyngeal nerveassociated with the carotid baroreceptors to fire at an increased ratein order to signal the brain to lower blood pressure. Similar modulationof the glossopharyngeal nerve may be achieved with a neuromodulatorimplanted in a subcutaneous location in a patient's neck or behind apatient's ear. A neuromodulator place in a renal artery may receive amodulation control signal tailored to cause an inhibiting or blockingsignal (i.e. a down modulation) at the electrodes, thereby inhibiting asignal to raise blood pressure carried from the renal nerves to thekidneys.

Modulation control signals may include stimulation control signals, andsub-modulation control signals may include sub-stimulation controlsignals. Stimulation control signals may have any amplitude, pulseduration, or frequency combination that results in a stimulation signalat electrodes 158 a, 158 b. In some embodiments (e.g., at a frequency ofbetween about 6.5-13.6 MHz), stimulation control signals may include apulse duration of greater than about 50 microseconds and/or an amplitudeof approximately 0.5 amps, or between 0.1 amps and 1 amp, or between0.05 amps and 3 amps. Sub-stimulation control signals may have a pulseduration less than about 500, or less than about 200 nanoseconds and/oran amplitude less than about 1 amp, 0.5 amps, 0.1 amps, 0.05 amps, or0.01 amps. Of course, these values are meant to provide a generalreference only, as various combinations of values higher than or lowerthan the exemplary guidelines provided may or may not result in nervestimulation.

In some embodiments, stimulation control signals may include a pulsetrain, wherein each pulse includes a plurality of sub-pulses. Analternating current signal (e.g., at a frequency of between about6.5-13.6 MHz) may be used to generate the pulse train, as follows. Asub-pulse may have a duration of between 50-250 microseconds, or aduration of between 1 microsecond and 2 milliseconds, during which analternating current signal is turned on. For example, a 200 microsecondsub-pulse of a 10 MHz alternating current signal will includeapproximately 2000 periods. Each pulse may, in turn, have a duration ofbetween 100 and 500 milliseconds, during which sub-pulses occur at afrequency of between 25 and 100 Hz. For example, a 200 millisecond pulseof 50 Hz sub-pulses will include approximately 10 sub-pulses. Finally,in a pulse train, each pulse may be separated from the next by aduration of between 0.2 and 2 seconds. For example, in a pulse train of200 millisecond pulses, each separated by 1.3 seconds from the next, anew pulse will occur every 1.5 seconds. A pulse train of this embodimentmay be utilized, for example, to provide ongoing stimulation during atreatment session. In the context of OSA, a treatment session may be aperiod of time during which a subject is asleep and in need of treatmentto prevent OSA. Such a treatment session may last anywhere from aboutthree to ten hours. In the context of other conditions to which neuralmodulators of the present disclosure are applied, a treatment sessionmay be of varying length according to the duration of the treatedcondition.

Processor 144 may be configured to determine a degree of couplingbetween primary antenna 150 and secondary antenna 152 by monitoring oneor more aspects of the primary coupled signal component received throughfeedback circuit 148. In some embodiments, processor 144 may determine adegree of coupling between primary antenna 150 and secondary antenna 152by monitoring a voltage level associated with the primary coupled signalcomponent, a current level, or any other attribute that may depend onthe degree of coupling between primary antenna 150 and secondary antenna152. For example, in response to periodic sub-modulation signals appliedto primary antenna 150, processor 144 may determine a baseline voltagelevel or current level associated with the primary coupled signalcomponent. This baseline voltage level, for example, may be associatedwith a range of movement of the patient's tongue when a sleep apneaevent or its precursor is not occurring, e.g. during normal breathing.As the patient's tongue moves toward a position associated with a sleepapnea event, moves in a manner consistent with a precursor of sleepapnea, or moves in any other manner (e.g., vibration, etc.), thecoaxial, lateral, or angular offset between primary antenna 150 andsecondary antenna 152 may change. As a result, the degree of couplingbetween primary antenna 150 and secondary antenna 152 may change, andthe voltage level or current level of the primary coupled signalcomponent on primary antenna 150 may also change. Processor 144 may beconfigured to recognize a sleep apnea event or its precursor when avoltage level, current level, or other electrical characteristicassociated with the primary coupled signal component changes by apredetermined amount or reaches a predetermined absolute value.

FIG. 7 provides a graph that illustrates this principle in more detail.For a two-coil system where one coil receives a radio frequency (RF)drive signal, graph 200 plots a rate of change in induced current in thereceiving coil as a function of coaxial distance between the coils. Forvarious coil diameters and initial displacements, graph 200 illustratesthe sensitivity of the induced current to further displacement betweenthe coils, moving them either closer together or further apart. It alsoindicates that, overall, the induced current in the secondary coil willdecrease as the secondary coil is moved away from the primary, drivecoil, i.e. the rate of change of induced current, in mA/mm, isconsistently negative. The sensitivity of the induced current to furtherdisplacement between the coils varies with distance. For example, at aseparation distance of 10 mm, the rate of change in current as afunction of additional displacement in a 14 mm coil is approximately −6mA/mm. If the displacement of the coils is approximately 22 mm, the rateof change in the induced current in response to additional displacementis approximately −11 mA/mm, which corresponds to a local maximum in therate of change of the induced current. Increasing the separationdistance beyond 22 mm continues to result in a decline in the inducedcurrent in the secondary coil, but the rate of change decreases. Forexample, at a separation distance of about 30 mm, the 14 mm coilexperiences a rate of change in the induced current in response toadditional displacement of about −8 mA/mm. With this type ofinformation, processor 144 may be able to determine a particular degreeof coupling between primary antenna 150 and secondary antenna 152, atany given time, by observing the magnitude and/or rate of change in themagnitude of the current associated with the primary coupled signalcomponent on primary antenna 150.

Processor 144 may be configured to determine a degree of couplingbetween primary antenna 150 and secondary antenna 152 by monitoringother aspects of the primary coupled signal component. For example, insome embodiments, the non-linear behavior of circuitry 180 in implantunit 110 may be monitored to determine a degree of coupling. Forexample, the presence, absence, magnitude, reduction and/or onset ofharmonic components in the primary coupled signal component on primaryantenna 150 may reflect the behavior of circuitry 180 in response tovarious control signals (either sub-modulation or modulation controlsignals) and, therefore, may be used to determine a degree of couplingbetween primary antenna 150 and secondary antenna 152.

As shown in FIG. 6, circuitry 180 in implant unit 110 may constitute anon-linear circuit due, for example, to the presence of non-linearcircuit components, such as diode 156. Such non-linear circuitcomponents may induce non-linear voltage responses under certainoperation conditions. Non-linear operation conditions may be inducedwhen the voltage potential across diode 156 exceeds the activationthreshold for diode 156. Thus, when implant circuitry 180 is excited ata particular frequency, this circuit may oscillate at multiplefrequencies. Spectrum analysis of the secondary signal or secondaryantenna 152, therefore, may reveal one or more oscillations, calledharmonics, that appear at certain multiples of the excitation frequency.Through coupling of primary antenna 150 and secondary antenna 152, anyharmonics produced by implant circuitry 180 and appearing on secondaryantenna 152 may also appear in the primary coupled signal componentpresent on primary antenna 150.

In certain embodiments, circuitry 180 may include additional circuitcomponents that alter the characteristics of the harmonics generated incircuitry 180 above a certain transition point. Monitoring how thesenon-linear harmonics behave above and below the transition point mayenable a determination of a degree of coupling between primary antenna150 and secondary antenna 152. For example, as shown in FIG. 6,circuitry 180 may include a harmonics modifier circuit 154, which mayinclude any electrical components that non-linearly alter the harmonicsgenerated in circuitry 180. In some embodiments, harmonics modifiercircuit 154 may include a pair of Zener diodes. Below a certain voltagelevel, these Zener diodes remain forward biased such that no currentwill flow through either diode. Above the breakdown voltage of the Zenerdiodes, however, these devices become conductive in the reversed biaseddirection and will allow current to flow through harmonics modifiercircuit 154. Once the Zener diodes become conductive, they begin toaffect the oscillatory behavior of circuitry 180, and, as a result,certain harmonic oscillation frequencies may be affected (e.g., reducedin magnitude).

FIGS. 8 and 9 illustrate this effect. For example, FIG. 8 illustrates agraph 300 a that shows the oscillatory behavior of circuitry 180 atseveral amplitudes ranging from about 10 nanoamps to about 20 microamps.As shown, the primary excitation frequency occurs at about 6.7 MHz andharmonics appear both at even and odd multiples of the primaryexcitation frequency. For example, even multiples appear at twice theexcitation frequency (peak 302 a), four times the excitation frequency(peak 304 a) and six times the excitation frequency (peak 306 a). As theamplitude of the excitation signal rises between 10 nanoamps and 40microamps, the amplitude of peaks 302 a, 304 a, and 306 a all increase.

FIG. 9 illustrates the effect on the even harmonic response of circuitry180 caused by harmonics modifier circuit 154. FIG. 9 illustrates a graph300 b that shows the oscillatory behavior of circuitry 180 at severalamplitudes ranging from about 30 microamps to about 100 microamps. As inFIG. 8, FIG. 9 shows a primary excitation frequency at about 6.7 MHz andsecond, fourth, and sixth order harmonics (peaks 302 b, 304 b, and 306b, respectively) appearing at even multiples of the excitationfrequency. As the amplitude of the excitation signal rises, however,between about 30 microamps to about 100 microamps, the amplitudes ofpeaks 302 b, 304 b, and 306 b do not continuously increase. Rather, theamplitude of the second order harmonics decreases rapidly above acertain transition level (e.g., about 80 microamps in FIG. 8). Thistransition level corresponds to the level at which the Zener diodesbecome conductive in the reverse biased direction and begin to affectthe oscillatory behavior of circuitry 180.

Monitoring the level at which this transition occurs may enable adetermination of a degree of coupling between primary antenna 150 andsecondary antenna 152. For example, in some embodiments, a patient mayattach external unit 120 over an area of the skin under which implantunit 110 resides. Processor 144 can proceed to cause a series ofsub-modulation control signals to be applied to primary antenna 150,which in turn cause secondary signals on secondary antenna 152. Thesesub-modulation control signals may progress over a sweep or scan ofvarious signal amplitude levels. By monitoring the resulting primarycoupled signal component on primary antenna 150 (generated throughcoupling with the secondary signal on secondary antenna 152), processor144 can determine the amplitude of primary signal (whether asub-modulation control signal or other signal) that results in asecondary signal of sufficient magnitude to activate harmonics modifiercircuit 154. That is, processor 144 can monitor the amplitude of thesecond, fourth, or sixth order harmonics and determine the amplitude ofthe primary signal at which the amplitude of any of the even harmonicsdrops. FIGS. 8 and 9 illustrate the principles of detecting couplingthrough the measurement of non-linear harmonics. These Figuresillustrate data based around a 6.7 MHz excitation frequency. Theseprinciples, however, are not limited to the 6.7 MHz excitation frequencyillustrated, and may be used with a primary signal of any suitablefrequency.

In embodiments utilizing non-linear harmonics, the determined amplitudeof the primary signal corresponding to the transition level of the Zenerdiodes (which may be referred to as a primary signal transitionamplitude) may establish the baseline coupling range when the patientattaches external unit 120 to the skin. A baseline coupling range mayalso encompass a range that does not include a maximum coupling levelbetween primary antenna 150 and secondary antenna 152. Thus, theinitially determined primary signal transition amplitude may be fairlyrepresentative of a non-sleep apnea condition and may be used byprocessor 144 as a baseline in determining a degree of coupling betweenprimary antenna 150 and secondary antenna 152. Optionally, processor 144may also be configured to monitor the primary signal transitionamplitude over a series of scans and select the minimum value as abaseline, as the minimum value may correspond to a condition of maximumcoupling between primary antenna 150 and secondary antenna 152 duringnormal breathing conditions.

As the patient wears external unit 120, processor 144 may periodicallyscan over a range of primary signal amplitudes to determine a currentvalue of the primary signal transition amplitude. In some embodiments,the range of amplitudes that processor 144 selects for the scan may bebased on (e.g., near) the level of the baseline primary signaltransition amplitude. If a periodic scan results in determination of aprimary signal transition amplitude different from the baseline primarysignal transition amplitude, processor 144 may determine that there hasbeen a change from the baseline initial conditions. For example, in someembodiments, an increase in the primary signal transition amplitude overthe baseline value may indicate that there has been a reduction in thedegree of coupling between primary antenna 150 and secondary antenna 152(e.g., because the implant has moved or an internal state of the implanthas changed).

In addition to determining whether a change in the degree of couplinghas occurred, processor 144 may also be configured to determine aspecific degree of coupling based on an observed primary signaltransition amplitude. For example, in some embodiments, processor 144may have access to a lookup table or a memory storing data thatcorrelates various primary signal transition amplitudes with distances(or any other quantity indicative of a degree of coupling) betweenprimary antenna 150 and secondary antenna 152. In other embodiments,processor 144 may be configured to calculate a degree of coupling basedon performance characteristics of known circuit components.

By periodically determining a degree of coupling value, processor 144may be configured to determine, in situ, appropriate parameter valuesfor the modulation control signal that will ultimately result in nervemodulation. For example, by determining the degree of coupling betweenprimary antenna 150 and secondary antenna 152, processor 144 may beconfigured to select characteristics of the modulation control signal(e.g., amplitude, pulse duration, frequency, etc.) that may provide amodulation signal at electrodes 158 a, 158 b in proportion to orotherwise related to the determined degree of coupling. In someembodiments, processor 144 may access a lookup table or other datastored in a memory correlating modulation control signal parametervalues with degree of coupling. In this way, processor 144 may adjustthe applied modulation control signal in response to an observed degreeof coupling.

Additionally or alternatively, processor 144 may be configured todetermine the degree of coupling between primary antenna 150 andsecondary antenna 152 during modulation. The tongue, or other structureon or near which the implant is located, and thus implant unit 110, maymove as a result of modulation. Thus, the degree of coupling may changeduring modulation. Processor 144 may be configured to determine thedegree of coupling as it changes during modulation, in order todynamically adjust characteristics of the modulation control signalaccording to the changing degree of coupling. This adjustment may permitprocessor 144 to cause implant unit 110 to provide an appropriatemodulation signal at electrodes 158 a, 158 b throughout a modulationevent. For example, processor 144 may alter the primary signal inaccordance with the changing degree of coupling in order to maintain aconstant modulation signal, or to cause the modulation signal to bereduced in a controlled manner according to patient needs.

More particularly, the response of processor 144 may be correlated tothe determined degree of coupling. In situations where processor 144determines that the degree of coupling between primary antenna 150 andsecondary antenna has fallen only slightly below a predeterminedcoupling threshold (e.g., during snoring or during a small vibration ofthe tongue or other sleep apnea event precursor), processor 144 maydetermine that only a small response is necessary. Thus, processor 144may select modulation control signal parameters that will result in arelatively small response (e.g., a short stimulation of a nerve, smallmuscle contraction, etc.). Where, however, processor 144 determines thatthe degree of coupling has fallen substantially below the predeterminedcoupling threshold (e.g., where the tongue has moved enough to cause asleep apnea event), processor 144 may determine that a larger responseis required. As a result, processor 144 may select modulation controlsignal parameters that will result in a larger response. In someembodiments, only enough power may be transmitted to implant unit 110 tocause the desired level of response. In other words, processor 144 maybe configured to cause a metered response based on the determined degreeof coupling between primary antenna 150 and secondary antenna 152. Asthe determined degree of coupling decreases, processor 144 may causetransfer of power in increasing amounts. Such an approach may preservebattery life in the external unit 120, may protect circuitry 170 andcircuitry 180, may increase effectiveness in addressing the type ofdetected condition (e.g., sleep apnea, snoring, tongue movement, etc.),and may be more comfortable for the patient.

In some embodiments, processor 144 may employ an iterative process inorder to select modulation control signal parameters that result in adesired response level. For example, upon determining that a modulationcontrol signal should be generated, processor 144 may cause generationof an initial modulation control signal based on a set of predeterminedparameter values. If feedback from feedback circuit 148 indicates that anerve has been modulated (e.g., if an increase in a degree of couplingis observed), then processor 144 may return to a monitoring mode byissuing sub-modulation control signals. If, on the other hand, thefeedback suggests that the intended nerve modulation did not occur as aresult of the intended modulation control signal or that modulation ofthe nerve occurred but only partially provided the desired result (e.g.,movement of the tongue only partially away from the airway), processor144 may change one or more parameter values associated with themodulation control signal (e.g., the amplitude, pulse duration, etc.).

Where no nerve modulation occurred, processor 144 may increase one ormore parameters of the modulation control signal periodically until thefeedback indicates that nerve modulation has occurred. Where nervemodulation occurred, but did not produce the desired result, processor144 may re-evaluate the degree of coupling between primary antenna 150and secondary antenna 152 and select new parameters for the modulationcontrol signal targeted toward achieving a desired result. For example,where stimulation of a nerve causes the tongue to move only partiallyaway from the patient's airway, additional stimulation may be desired.Because the tongue has moved away from the airway, however, implant unit110 may be closer to external unit 120 and, therefore, the degree ofcoupling may have increased. As a result, to move the tongue a remainingdistance to a desired location may require transfer to implant unit 110of a smaller amount of power than what was supplied prior to the laststimulation-induced movement of the tongue. Thus, based on a newlydetermined degree of coupling, processor 144 can select new parametersfor the stimulation control signal aimed at moving the tongue theremaining distance to the desired location.

In one mode of operation, processor 144 may be configured to sweep overa range of parameter values until nerve modulation is achieved. Forexample, in circumstances where an applied sub-modulation control signalresults in feedback indicating that nerve modulation is appropriate,processor 144 may use the last applied sub-modulation control signal asa starting point for generation of the modulation control signal. Theamplitude and/or pulse duration (or other parameters) associated withthe signal applied to primary antenna 150 may be iteratively increasedby predetermined amounts and at a predetermined rate until the feedbackindicates that nerve modulation has occurred.

Processor 144 may be configured to determine or derive variousphysiologic data based on the determined degree of coupling betweenprimary antenna 150 and secondary antenna 152. For example, in someembodiments the degree of coupling may indicate a distance betweenexternal unit 120 and implant unit 110, which processor 144 may use todetermine a position of external unit 120 or a relative position of apatient's tongue. Monitoring the degree of coupling can also providesuch physiologic data as whether a patient's tongue is moving orvibrating (e.g., whether the patient is snoring), by how much the tongueis moving or vibrating, the direction of motion of the tongue, the rateof motion of the tongue, etc.

In response to any of these determined physiologic data, processor 144may regulate delivery of power to implant unit 110 based on thedetermined physiologic data. For example, processor 144 may selectparameters for a particular modulation control signal or series ofmodulation control signals for addressing a specific condition relatingto the determined physiologic data. If the physiologic data indicatesthat the tongue is vibrating, for example, processor 144 may determinethat a sleep apnea event is likely to occur and may issue a response bydelivering power to implant unit 110 in an amount selected to addressthe particular situation. If the tongue is in a position blocking thepatient's airway (or partially blocking a patient's airway), but thephysiologic data indicates that the tongue is moving away from theairway, processor 144 may opt to not deliver power and wait to determineif the tongue clears on its own. Alternatively, processor 144 maydeliver a small amount of power to implant unit 110 (e.g., especiallywhere a determined rate of movement indicates that the tongue is movingslowly away from the patient's airway) to encourage the tongue tocontinue moving away from the patient's airway or to speed itsprogression away from the airway. Additionally or alternatively,processor 144 may deliver power to implant unit 110 to initiate a tonguemovement, monitor the movement of the tongue, and deliver additionalpower, for example, a reduced amount of power, if necessary to encouragethe tongue to continue moving away from the patient's airway. Thescenarios described are exemplary only. Processor 144 may be configuredwith software and/or logic enabling it to address a variety of differentphysiologic scenarios with particularity. In each case, processor 144may be configured to use the physiologic data to determine an amount ofpower to be delivered to implant unit 110 in order to modulate nervesassociated with the tongue with the appropriate amount of energy.

The disclosed embodiments may be used in conjunction with a method forregulating delivery of power to an implant unit. The method may includedetermining a degree of coupling between primary antenna 150 associatedwith external unit 120 and secondary antenna 152 associated with implantunit 110, implanted in the body of a patient. Determining the degree ofcoupling may be accomplished by processor 144 located external toimplant unit 110 and that may be associated with external unit 120.Processor 144 may be configured to regulate delivery of power from theexternal unit to the implant unit based on the determined degree ofcoupling.

As previously discussed, the degree of coupling determination may enablethe processor to further determine a location of the implant unit. Themotion of the implant unit may correspond to motion of the body partwhere the implant unit may be attached. This may be consideredphysiologic data received by the processor. The processor may,accordingly, be configured to regulate delivery of power from the powersource to the implant unit based on the physiologic data. In alternativeembodiments, the degree of coupling determination may enable theprocessor to determine information pertaining to a condition of theimplant unit. Such a condition may include location as well asinformation pertaining to an internal state of the implant unit. Theprocessor may, according to the condition of the implant unit, beconfigured to regulate delivery of power from the power source to theimplant unit based on the condition data.

In some embodiments, implant unit 110 may include a processor located onthe implant. A processor located on implant unit 110 may perform all orsome of the processes described with respect to the at least oneprocessor associated with an external unit. For example, a processorassociated with implant unit 110 may be configured to receive a controlsignal prompting the implant controller to turn on and cause amodulation signal to be applied to the implant electrodes for modulatinga nerve. Such a processor may also be configured to monitor varioussensors associated with the implant unit and to transmit thisinformation back to and external unit. Power for the processor unit maybe supplied by an onboard power source or received via transmissionsfrom an external unit.

In other embodiments, implant unit 110 may be self-sufficient, includingits own power source and a processor configured to operate the implantunit 110 with no external interaction. For example, with a suitablepower source, the processor of implant unit 110 could be configured tomonitor conditions in the body of a subject (via one or more sensors orother means), determining when those conditions warrant modulation of anerve, and generate a signal to the electrodes to modulate a nerve. Thepower source could be regenerative based on movement or biologicalfunction; or the power sources could be periodically rechargeable froman external location, such as, for example, through induction.

In some embodiments, the at least one processor may be associated withthe housing of external unit 120 and may be configured to communicatewith a circuit implanted in the subject. The at least one processor mayalso be configured to receive a physiological signal from the subjectvia the implanted circuit. In response to the received physiologicalsignal, the at least one processor may send a control signal, such as aclosed loop control signal, to the implanted circuit. In someembodiments, the control signal may be predetermined to activateneuromuscular tissue within the tongue. Activating neuromuscular tissuemay include, for example, causing muscular contractions and initiating anerve action potential.

The physiological signal received from the implant unit may include anysignal or signal component indicative of at least one physiologicalcharacteristic associated with the subject. In some embodiments, forexample, the physiological characteristic may indicate whether a portionof the subject's body (e.g., the tongue) has moved, a direction ofmovement, a rate of change of movement, temperature, blood pressure,etc. The physiological signal may include any form of signal suitablefor conveying information associated with at least some aspect of thesubject. In some embodiments, the physiological signal may include anelectromagnetic signal (e.g. microwave, infrared, radio-frequency (RF),etc.) having any desired waveform (e.g. sinusoidal, square wave,triangle wave, etc.). In some embodiments, the physiological signal mayinclude any suitable amplitude or duration for transferring informationabout the subject.

In some embodiments, the physiological signal may include a primarycoupled signal component on primary antenna 150. This primary coupledsignal component may be induced on primary antenna 150 through couplingbetween primary antenna 150 of external unit 120 and secondary antenna152 on implant unit 110.

In some embodiments, the physiological signal may include at least oneaspect indicative of a movement of the subject's tongue. For example,movement of the tongue may cause relative motion between primary antenna150 and secondary antenna 152, and this relative motion may result invariation of a degree of coupling between primary antenna 150 andsecondary antenna 152. By monitoring the degree of coupling betweenprimary antenna 150 and secondary antenna 152, for example, bymonitoring signals or signal components present on primary antenna 150,relative motion between primary antenna 150 and secondary antenna 152and, therefore, movement of the subject's tongue, may be detected.

As noted, in response to a received physiological signal, the at leastone processor may cause a response based on the physiological signal.For example, in some embodiments, the at least one processor may beconfigured to cause the generation of a control signal (e.g. a closedloop control signal) intended to control at least one aspect of implantunit 110. The control signal may include a modulation control signalapplied to primary antenna 150 such that a resulting secondary signal onsecondary antenna 152 will provide a modulation signal at implantelectrodes 158 a and 158 b.

In some embodiments, the processor may be configured to detect a sleepdisordered breathing event based on the physiological signal and sendthe closed loop control signal in response to the detected sleepdisordered breathing event. In some embodiments, the sleep disorderedbreathing event may be a precursor of sleep apnea, and the controlsignal may be predetermined to activate neuromuscular tissue within thetongue and may cause movement of the subject's tongue, for example, in adirection away from the posterior pharyngeal wall. The at least oneprocessor may be further configured to determine a severity of the sleepdisordered breathing event based on the physiological signal and vary apower level or duration of the control signal based on the determinedseverity of the sleep disordered breathing event. The severity of theevent may be determined, for example, based on a determination of therelative movement between primary antenna 150 and secondary antenna 152(e.g., an amplitude of movement, a rate of movement, a direction ofmovement, etc.). In some embodiments, a control signal may be sent ifthe relative movement exceeds a certain threshold.

A control signal may include any signal having suitable characteristicsfor causing a desired response in implant unit 110. For example, acontrol signal may have any suitable amplitude, duration, pulse width,duty cycle, or waveform (e.g. a sinusoidal signal, square wave, trianglewave, etc.) for causing a desired effect on implant unit 110 (e.g.,modulation of nerve tissue in the vicinity of implant unit 110, etc.). Acontrol signal may be generated and sent (e.g., to implant unit 110)within any desired response time relative to receipt of a physiologicalsignal. In some embodiments, the response time may be set at 1 second,500 milliseconds, 200 milliseconds, 100 milliseconds, 50 milliseconds,20 milliseconds, 5 milliseconds, 1 millisecond, or any other timegreater than 0 seconds and less than about 2 seconds. The control signalmay be closed loop. As used herein, the term closed loop control signalmay refer to any signal at least partially responsive to another signal,such as a control signal sent in response to a physiological signal. Orit may include any feedback response.

Based on the physiological signal, the processor may determine aquantity of energy to be sent via the closed loop control signal toimplant unit 110. The amount of energy to be sent may be determinedand/or varied based on any relevant factor including, for example, thetime of day, a relevant biological factor of the subject (bloodpressure, pulse, level of brain activity, etc.), the severity of thedetected event, other characteristics associated with the detectedevent, or on any combination of factors. As noted, in embodiments wherethe physiological signal indicates a sleep disordered breathing event,the processor may be configured to determine a severity of the sleepdisordered breathing event based on the physiological signal. In suchembodiments, the processor may also determine an amount of energy to beprovided to implant unit 110 as a response to the detected sleepdisordered breathing event and in view of the determined severity of theevent. The determined amount of energy may be transferred to implantunit 110 over any suitable time duration and at any suitable powerlevel. In some embodiments, the power level and/or the duration of thecontrol signal may be varied, and such variation may be dependent on thedetermined severity of the sleep disordered breathing event.

The power level and/or duration of the control signal may also bedetermined based on other factors. For example, the processor may vary apower level or duration associated with the control signal based on theefficiency of energy transfer between external unit 120 and Implant unit110. The processor may have access to such Information throughpre-programming, lookup tables, information stored in memory, etc.Additionally or alternatively, the processor may be configured todetermine the efficiency of energy transfer, e.g., by monitoring theprimary coupled signal component present on primary antenna 150, or byany other suitable method.

The processor may also vary the power level or duration of the controlsignal based on the efficacy of implant unit 110 (e.g., the implantunit's ability to produce a desired effect in response to the controlsignal). For example, the processor may determine that a certain implantunit 110 requires a certain amount of energy, a control signal of atleast a certain power level and/or signal duration, etc., in order toproduce a desired response (e.g., a modulation signal having anamplitude/magnitude of at least a desired level, etc.). Such adetermination can be based on feedback received from implant unit 110 ormay be determined based on lookup tables, information stored in memory,etc. In some embodiments, the power level or duration of the controlsignal may be determined based on a known or feedback-determinedefficacy threshold (e.g., an upper threshold at or above which a desiredresponse may be achieved) associated with implant unit 110.

In some embodiments, implant unit 110 may be structurally configured tofacilitate implantation in a location so as to increase the efficacy ofmodulation provided. For example, FIGS. 10 and 11 illustrate the anatomyof neck and tongue, and depict implantation locations suitable forneuromodulation treatment of OSA. FIG. 14 illustrates an exemplaryimplant unit 110 structurally configured for the treatment of head pain.FIGS. 15 and 16 illustrate exemplary implant units 110 structurallyconfigured for the treatment of hypertension.

FIG. 12 depicts an implantation location in the vicinity of agenioglossus muscle 1060 that may be accessed through derma on anunderside of a subject's chin. FIG. 12 depicts hypoglossal nerve (i.e.cranial nerve XII). The hypoglossal nerve 1051, through its lateralbranch 1053 and medial branch 1052, innervates the muscles of the tongueand other glossal muscles, including the genioglossus 1060, thehyoglossus 1062, mylohyoid (not shown) and the geniohyoid 1061 muscles.The mylohyoid muscle, not pictured in FIG. 12, forms the floor of theoral cavity, and wraps around the sides of the genioglossus muscle 1060.and the geniohyoid 1061 muscles. The horizontal compartment of thegenioglossus 1060 is mainly innervated by the medial terminal fibers1054 of the medial branch 1052, which diverges from the lateral branch1053 at terminal bifurcation 1055. The distal portion of medial branch1052 then variegates into the medial terminal fibers 1054. Contractionof the horizontal compartment of the genioglossus muscle 1060 may serveto open or maintain a subject's airway. Contraction of other glossalmuscles may assist in other functions, such as swallowing, articulation,and opening or closing the airway. Because the hypoglossal nerve 1051innervates several glossal muscles, it may be advantageous, for OSAtreatment, to confine modulation of the hypoglossal nerve 1051 to themedial branch 1052 or even the medial terminal fibers 1054 of thehypoglossal nerve 1051. In this way, the genioglossus muscle, mostresponsible for tongue movement and airway maintenance, may beselectively targeted for contraction inducing neuromodulation.Alternatively, the horizontal compartment of the genioglossus muscle maybe selectively targeted. The medial terminal fibers 1054 may, however,be difficult to affect with neuromodulation, as they are located withinthe fibers of the genioglossus muscle 1061. Embodiments of the presentinvention facilitate modulation the medial terminal fibers 1054, asdiscussed further below.

In some embodiments, implant unit 110, including at least one pair ofmodulation electrodes, e.g. electrodes 158 a, 158 b, and at least onecircuit may be configured for implantation through derma (i.e. skin) onan underside of a subject's chin. When implanted through derma on anunderside of a subject's chin, an implant unit 110 may be locatedproximate to medial terminal fibers 1054 of the medial branch 1052 of asubject's hypoglossal nerve 1051. An exemplary implant location 1070 isdepicted in FIG. 12.

In some embodiments, implant unit 110 may be configured such that theelectrodes 158 a, 158 b cause modulation of at least a portion of thesubject's hypoglossal nerve through application of an electric field toa section of the hypoglossal nerve 1051 distal of a terminal bifurcation1055 to lateral and medial branches 1053, 1052 of the hypoglossal nerve1051. In additional or alternative embodiments, implant unit 110 may belocated such that an electric field extending from the modulationelectrodes 158 a, 158 b can modulate one or more of the medial terminalfibers 1054 of the medial branch 1052 of the hypoglossal nerve 1051.Thus, the medial branch 1053 or the medial terminal fibers 1054 may bemodulated so as to cause a contraction of the genioglossus muscle 1060,which may be sufficient to either open or maintain a patient's airway.When implant unit 110 is located proximate to the medial terminal fibers1054, the electric field may be configured so as to cause substantiallyno modulation of the lateral branch of the subject's hypoglossal nerve1051. This may have the advantage of providing selective modulationtargeting of the genioglossus muscle 1060.

As noted above, it may be difficult to modulate the medial terminalfibers 1054 of the hypoglossal nerve 1051 because of their locationwithin the genioglossus muscle 1060. Implant unit 110 may be configuredfor location on a surface of the genioglossus muscle 1060. Electrodes158 a, 158 b, of implant unit 110 may be configured to generate aparallel electric field 1090, sufficient to cause modulation of themedial terminal branches 1054 even when electrodes 158 a, 158 b are notin contact with the fibers of the nerve. That is, the anodes and thecathodes of the implant may be configured such that, when energized viaa circuit associated with the implant 110 and electrodes 158 a, 158 b,the electric field 1090 extending between electrodes 158 a, 158 b may bein the form of a series of substantially parallel arcs extending throughand into the muscle tissue on which the implant is located. A pair ofparallel line electrodes or two series of circular electrodes may besuitable configurations for producing the appropriate parallel electricfield lines. Thus, when suitably implanted, the electrodes of implantunit 110 may modulate a nerve in a contactless fashion, through thegeneration of parallel electric field lines.

Furthermore, the efficacy of modulation may be increased by an electrodeconfiguration suitable for generating parallel electric field lines thatrun partially or substantially parallel to nerve fibers to be modulated.In some embodiments, the current induced by parallel electric fieldlines may have a greater modulation effect on a nerve fiber if theelectric field lines 1090 and the nerve fibers to be modulated arepartially or substantially parallel. The inset illustration of FIG. 12depicts electrodes 158 a and 158 b generating electric field lines 1090(shown as dashed lines) substantially parallel to medial terminal fibers1054.

In order to facilitate the modulation of the medial terminal fibers1054, implant unit 110 may be designed or configured to ensure theappropriate location of electrodes when implanted. An exemplaryimplantation is depicted in FIG. 13.

For example, a flexible carrier 161 of the implant may be configuredsuch that at least a portion of a flexible carrier 161 of the implant islocated at a position between the genioglossus muscle 1060 and thegeniohyoid muscle 1061. Flexible carrier 161 may be further configuredto permit at least one pair of electrodes arranged on flexible carrier161 to lie between the genioglossus muscle 1060 and the mylohyoidmuscle. Either or both of the extensions 162 a and 162 b of elongate arm161 may be configured adapt to a contour of the genioglossus muscle.Either or both of the extensions 162 a and 162 b of elongate arm 161 maybe configured to extend away from the underside of the subject's chinalong a contour of the genioglossus muscle 1060. Either or both ofextension arms 162 a, 162 b may be configured to wrap around thegenioglossus muscle when an antenna 152 is located between thegenioglossus 1060 and geniohyoid muscle 1061. In such a configuration,antenna 152 may be located in a plane substantially parallel with aplane defined by the underside of a subject's chin, as shown in FIG. 13.

Flexible carrier 161 may be configured such that the at least one pairof spaced-apart electrodes can be located in a space between thesubject's genioglossus muscle and an adjacent muscle. Flexible carrier161 may be configured such that at least one pair of modulationelectrodes 158 a, 158 b is configured for implantation adjacent to ahorizontal compartment 1065 of the genioglossus muscle 1060. Thehorizontal compartment 1065 of the genioglossus 1060 is depicted in FIG.13 and is the portion of the muscle in which the muscle fibers run in asubstantially horizontal, rather than vertical, oblique, or transversedirection. At this location, the hypoglossal nerve fibers run betweenand in parallel to the genioglossus muscle fibers. In such a location,implant unit 110 may be configured such that the modulation electrodesgenerate an electric field substantially parallel to the direction ofthe muscle fibers, and thus, the medial terminal fibers 1054 of thehypoglossal nerve in the horizontal compartment.

FIG. 14 depicts an exemplary implant location for the treatment of headpain. As illustrated in FIG. 14, implant unit 510 includes an elongatedcarrier 561, secondary antenna 552, and modulation electrodes 558 a, 558b. Implant unit 510 may also include any elements, such as circuitry,electrical components, materials, and any other features describedpreviously with respect to implant unit 110. Implant 510 may be sizedand configured such that it may be implanted with an end havingsecondary antenna 552 located beneath the skin in a substantiallyhairless region 507 of a subject. Elongated flexible carrier 561 mayextend from this location, across a hairline 502 of the subject, to alocation beneath the skin in a substantially haired region 506 of thesubject in a vicinity of an occipital or other nerve that may bemodulated to control or reduce head pain, such as a greater occipitalnerve 501 or a lesser occipital nerve 503. As used herein, the term“substantially haired region” includes areas of a subject's head locatedon a side of the hairline where the scalp hair is located on a typicalsubject. Thus, a bald person may still have a “substantially hairedregion” on the side of the hairline on which hair typically grows. Asused herein, the term “substantially hairless region” includes areas ofa subject's head located on a side of the hairline where the scalp hairis not located on a typical subject. A “substantially hairless region,”as used herein, is not required to be completely hairless, as almost allskin surfaces have some hair growth. As illustrated in FIG. 14, asubstantially haired region 506 is separated from a substantiallyhairless region 507 by a hairline 502.

As described above, implant 510 may extend across the hairline 502 to alocation in the vicinity of an occipital nerve. In FIG. 14, implant 510extends across the hairline 502 to a location in the vicinity of greateroccipital nerve 501. Furthermore, implant 510 may be configured forimplantation such that electrodes 558 a and 558 b are spaced from eachother along a longitudinal direction of an occipital nerve, such as thegreater occipital nerve 501 shown in FIG. 14. Such a configurationpermits electrodes 558 a and 558 b to facilitate an electrical fieldthat extends in the longitudinal direction of the occipital nerve. Inturn, the facilitated electrical field may be utilized to modulategreater occipital nerve 501, for example to block pain signals, aspreviously described.

The size and configuration of implant 510 illustrated in FIG. 14 maypermit secondary antenna 552 to be located beneath the skin in alocation where an external unit 520 (not illustrated), may be easilyaffixed to the skin, due to the lack of hair. External unit 520 mayinclude any elements, such as circuitry, processors, batteries,antennas, electrical components, materials, and any other featuresdescribed previously with respect to external unit 120. External unit520 may be configured to communicate with implant 510 via secondaryantenna 552 to deliver power and control signals, as described abovewith respect to external unit 120. Elongated carrier 561 may beflexible, and may permit modulation electrodes 558 a and 558 b to belocated beneath the skin in a location suitable for modulating anoccipital or other nerve for controlling head pain.

FIG. 15 depicts an exemplary implant location for the treatment ofhypertension. As illustrated in FIG. 15, implant unit 610 may beconfigured for location or implantation inside a blood vessel. Such aconfiguration may include, for example, a flexible tubular carrier.Implant unit 610 may also include any elements, such as circuitry,electrical components, materials, and any other features describedpreviously with respect to implant unit 110. Implant unit 610 mayinclude modulation electrodes 658 a, 658 b configured to facilitate anelectric field including field lines extending in the longitudinaldirection of the blood vessel. For example, as illustrated in FIG. 15,implant unit 610 may be implanted in a carotid artery 611. Implant unit610 may be located within carotid artery 611 in a location in thevicinity of carotid baroreceptors 615, at a location near the branchingof the internal carotid artery 613 and the external carotid artery 612.As described previously, carotid baroreceptors 615 aid in the regulationof the blood pressure of a subject. Thus, implant unit 610, locatedwithin carotid artery 611 in the vicinity of carotid baroreceptors 615may facilitate an electric field configured to modulate carotidbaroreceptors 615, and, thus, affect the blood pressure of a subject.Affecting the blood pressure of a subject may include reducing,increasing, controlling, regulating, and influencing the blood pressureof a subject. The illustrated location is exemplary only, and implantunit 610 may be configured in alternate ways. For example, implant unit610 may be configured for implantation in jugular vein 614 of thesubject, in a location from which modulation of carotid baroreceptors615 may be accomplished. Furthermore, implant unit 610 may be configuredfor implantation in a blood vessel, such as carotid artery 611 orjugular vein 614, in a location suitable for modulation ofglossopharyngeal nerve 615. As described above, glossopharyngeal nerve615 innervates carotid baroreceptors 615. Thus, glossopharyngeal nerve615 may be directly modulated to affect blood pressure of a subject.Glossopharyngeal nerve 615 may also be modulated by an implant unit 610located in a sub-cutaneously, in a non-intravascular location.

FIG. 16 depicts another exemplary implant location for the treatment ofhypertension. As illustrated in FIG. 16, implant unit 710 may beconfigured for location or implantation inside a blood vessel. Such aconfiguration may include, for example, a flexible tubular carrier.Implant unit 710 may also include any elements, such as circuitry,electrical components, materials, and any other features describedpreviously with respect to implant unit 110. Implant unit 710 mayinclude modulation electrodes 758 a, 758 b configured to facilitate anelectric field including field lines extending in the longitudinaldirection of the blood vessel. For example, as illustrated in FIG. 13,implant unit 710 may be implanted in a renal artery 711. Implant unit710 may be located within renal artery 711 in a location in the vicinityof renal nerves 715 surrounding renal artery 711 prior to its entry intokidney 712. As described previously, renal nerves 715 aids in theregulation of the blood pressure in humans. Thus, implant unit 710,located within renal artery 711 in the vicinity of renal nerves 715 mayfacilitate an electric field configured to modulate renal nerves 715,and, thus, affect the blood pressure of a subject. The illustratedlocation is exemplary only, and implant unit 710 may be configured inalternate ways suitable for the modulation of renal nerves 715.

Additional embodiments of the present disclosure may include a method ofmodulating a nerve via at least one pair of electrodes associated withan implanted circuit and implanted in the vicinity of the nerve. Themethod may include steps of delivering to the electrodes, via theimplanted circuit, an electrical signal having a current less than about1.6 milliamps and modulating the nerve via the generation of anelectrical field between the electrodes by the electrical signal havinga current less than about 1.6 milliamps. The method may further includedelivering a plurality of electrical signals to the electrodes, whereineach of the plurality of electrical signals has a current less thanabout 1.6 milliamps. The method may further include, further comprisingvarying at least one of a voltage, current, or duration of the pluralityof electrical signals. The method may further include receiving, via theimplantable circuit, energy from a source external to a subject. Themethod may further include delivering to the electrodes, via theelectrical signal having a current less than about 1.6 milliamps, asubstantial portion of the energy received from the source external tothe subject within about 1 second or less of receiving the energy. Themethod may further include providing an implantable antenna, inelectrical communication with the implantable circuit, for transmittingor receiving electrical signals. The method may further includegenerating and sending, via a transmitter included in the implantablecircuit, a signal indicative of a request that energy be supplied fromthe source external to the subject. The implantable circuit may beconfigured for location detection from a location external to thesubject. The circuit and the electrodes may be further configured forimplantation in a subject on the surface of non-nerve tissue interposedbetween the electrodes and the nerve. The tissue interposed between theelectrodes and the nerve may include at least one of muscle tissue,connective tissue, fat, blood vessel, and mucosal membrane.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present disclosure.

While this disclosure provides examples of the neuromodulation devicesemployed for the treatment of certain conditions, usage of the disclosedneuromodulation devices is not limited to the disclosed examples. Thedisclosure of uses of embodiments of the invention for neuromodulationare to be considered exemplary only. In its broadest sense, theinvention may be used in connection with the treatment of anyphysiological condition through neuromodulation. Alternative embodimentswill become apparent to those skilled in the art to which the presentinvention pertains without departing from its spirit and scope.Accordingly, the scope of the present invention is defined by theappended claims rather than the foregoing description.

What is claimed:
 1. A device, comprising: an implantable circuit; atleast one pair of implantable electrodes, electrically connected withthe implantable circuit, wherein the circuit and the electrodes areconfigured for implantation in a subject in the vicinity of a nerve; andwherein the circuit is configured to deliver to the electrodes anelectrical signal having a current less than about 1.6 milliamps,wherein the circuit includes a harmonics modifier circuit configured toalter a harmonic signal generated in the circuit, an implantable antennaconfigured to transmit the altered harmonic signal generated in thecircuit to a processor for determining a coupling between theimplantable antenna and an external antenna based on non-linear behaviorreflected by the altered harmonic signal, wherein the implantableantenna is configured to generate a signal having a magnitude greaterthan a predetermined threshold to activate the harmonics modifiercircuit; wherein the circuit and the electrodes are configured forimplantation in an implantation location in the subject on a surface ofnon-nerve tissue interposed between the electrodes and the nerve; andwherein the electrodes are further configured to emit an electric fieldsuch that a portion of the field lines extend along a length of thenerve such that the delivery of the electrical signal of less than about1.6 milliamps causes modulation of the nerve through the interposednon-nerve tissue from the implantation location spaced apart from thenerve and external to a blood vessel.
 2. The device of claim 1, whereinthe tissue interposed between the electrodes and the nerve includesmuscle tissue.
 3. The device of claim 1, wherein the implantable circuitis configured to deliver a plurality of electrical signals to theelectrodes, and wherein each of the plurality of electrical signals hasa current less than about 1.6 milliamps.
 4. The device of claim 3,wherein the plurality of electrical signals include various voltagelevels, current levels, or durations.
 5. The device of claim 1, whereinthe implantable circuit is configured to receive energy from a sourceexternal to a subject.
 6. The device of claim 5, wherein the implantablecircuit is configured to deliver to the electrodes, via the electricalsignal having a current less than about 1.6 milliamps, a substantialportion of the energy received from the source external to the subjectwithin about 1 second or less of receiving the energy.
 7. The device ofclaim 1, wherein the implantable circuit is in electrical communicationwith the implantable antenna for transmitting or receiving electricalsignals.
 8. The device of claim 1, wherein the coupling between the twoantennas enables the processor to determine the implantation location ofthe circuit under a skin of the subject.
 9. The device of claim 1,wherein the tissue interposed between the electrodes and the nerveincludes genioglossus muscle tissue.
 10. The device of claim 1, whereinthe electrical signal having a current less than about 1.6 milliamps hasa current less than about 1 milliamp.
 11. The device of claim 1, whereinthe electrical signal having a current less than about 1.6 milliamp hasa current less than about 0.8 milliamps.
 12. The device of claim 1,wherein the electrical signal having a current less than about 1.6milliamp has a current less than about 0.6 milliamps.
 13. The device ofclaim 1, wherein the electrical signal having a current less than about1.6 milliamp has a current less than about 0.4 milliamps.
 14. The deviceof claim 1, wherein the electrical signal having a current less thanabout 1.6 milliamp has a current less than about 0.2 milliamps.
 15. Thedevice of claim 1, wherein the tissue interposed between the electrodesand the nerve includes connective tissue.
 16. The device of claim 1,wherein the tissue interposed between the electrodes and the nerveincludes fat.
 17. The device of claim 1, wherein the tissue interposedbetween the electrodes and the nerve includes blood vessel tissue. 18.The device of claim 1, wherein the harmonics modifier circuit isconfigured to cause a decrease in magnitude of the harmonic signal at apredetermined frequency as an amplitude of an excitation signalincreases beyond a predetermined level.
 19. The device of claim 1,wherein the circuit includes a power limiting component configured tolimit a level of power the circuit outputs to the electrodes.
 20. Thedevice of claim 1, wherein the implantable antenna is mounted onto orintegrated with a flexible carrier.